RFR: 8345074: java.net.InterfaceAddress constructor could be made private

[Eirik Bjørsnøs]

Please review this PR which suggests to make the constructor of `java.net.InterfaceAddress` private.

This constructor is only accessed by native code via the `NetworkInterface` class. Making it private would express the intent of this class as being non-subclassable.

The comment of the constructor is updated to reflect the new access modifier as well as to make it clear that the constructor is not to be invoked from Java code and that instances are obtained from `NetworkInterface` via native code. 

Marking this class final is handled separately in JDK-8344943 via a CSR.

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Commit messages:
 - Make InterfaceAddress constructor private

Changes: https://git.openjdk.org/jdk/pull/22467/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22467&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345074
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/22467.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22467/head:pull/22467

PR: https://git.openjdk.org/jdk/pull/22467