HDFS-17877. DatanodeID.updateRegInfo() does not update hostNameBytes causing stale hostname on client

[eubnara]

Description of PR

DataNodeID.updateRegInfo() updates hostName but misses hostNameBytes.

Since PBHelperClient.convert(DatanodeID) uses getHostNameBytes() for protobuf
serialization, clients end up receiving the stale hostname from before the
re-registration.

This becomes a real problem when a DataNode first registers with a PQDN and
later re-registers with a FQDN. With dfs.client.use.datanode.hostname=true,
the client tries to connect using the old PQDN and fails with
UnknownHostException.

The fix is to add hostNameBytes = nodeReg.getHostNameBytes() in updateRegInfo(),
same as how setIpAndXferPort() already handles ipAddr/ipAddrBytes together

How was this patch tested?

• manual test on the private cluster
• add an unit test

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

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If an AI tool was used:

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[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	1m 16s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ trunk Compile Tests _
+1 💚	mvninstall	49m 17s		trunk passed
+1 💚	compile	1m 18s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	compile	1m 18s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	checkstyle	0m 50s		trunk passed
+1 💚	mvnsite	1m 22s		trunk passed
+1 💚	javadoc	1m 6s		trunk passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javadoc	1m 3s		trunk passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	spotbugs	3m 55s		trunk passed
+1 💚	shadedclient	36m 55s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 55s		the patch passed
+1 💚	compile	0m 49s		the patch passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javac	0m 49s		the patch passed
+1 💚	compile	0m 50s		the patch passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	javac	0m 50s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 19s		the patch passed
+1 💚	mvnsite	0m 55s		the patch passed
+1 💚	javadoc	0m 37s		the patch passed with JDK Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
+1 💚	javadoc	0m 36s		the patch passed with JDK Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
+1 💚	spotbugs	3m 37s		the patch passed
+1 💚	shadedclient	35m 23s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	2m 37s		hadoop-hdfs-client in the patch passed.
+1 💚	asflicense	0m 35s		The patch does not generate ASF License warnings.
		149m 46s

Subsystem	Report/Notes
Docker	ClientAPI=1.53 ServerAPI=1.53 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8216/1/artifact/out/Dockerfile
GITHUB PR	#8216
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux ef33fd9fb1b7 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14 20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 50bdae7
Default Java	Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Multi-JDK versions	/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 /usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8216/1/testReport/
Max. process+thread count	573 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs-client U: hadoop-hdfs-project/hadoop-hdfs-client
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8216/1/console
versions	git=2.25.1 maven=3.9.11 spotbugs=4.9.7
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