RFR: JDK-8264111 (fs) Leaking NativeBuffers in case of errors during UnixUserDefinedFileAttributeView.read/write

[Sebastian Stenzel]

Added new private methods for `read(String name, long address, int rem)` and `write(String name, long address, int rem)` that take an address as an argument and thereby no longer need to deal with any NativeBuffers.

This allows a certain simplification of `read(String name, ByteBuffer dst)` and `write(String name, ByteBuffer src)` and use of `try (NativeBuffer nb = NativeBuffers.getNativeBuffer(rem)) {...}` which fixes the issue.

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Commit messages:
 - refactor read and write to use try-with-resource for NativeBuffer

Changes: https://git.openjdk.java.net/jdk/pull/3171/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3171&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264111
  Stats: 86 lines in 1 file changed: 24 ins; 27 del; 35 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3171.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3171/head:pull/3171

PR: https://git.openjdk.java.net/jdk/pull/3171