RFR: 8284890: Support for Do not fragment IP socket options

[Michael McMahon]

Hi,

Could I get the following PR review please? It adds a new JDK specific extended socket option
called IP_DONTFRAGMENT, which disables IP packet fragmentation in both IPv4 and IPv6
UDP sockets (NIO DatagramChannels). For IPv4 in particular, it sets the DF (Dont Fragment) bit
in the IP header. There is no equivalent in the IPv6 packet header as fragmentation is implemented
exclusively by the sending and receiving nodes.

Thanks,
Michael

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Commit messages:
 - fix whitespace errors
 - minor spec update
 - windows 2016 issue
 - windows issue
 - windows update
 - test update
 - updates
 - simplified test. Loosened spec
 - Merge branch 'master' into mtu
 - fixed test
 - ... and 11 more: https://git.openjdk.java.net/jdk/compare/40ddb755...446dd6cf

Changes: https://git.openjdk.java.net/jdk/pull/8245/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8245&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284890
  Stats: 437 lines in 11 files changed: 434 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8245.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8245/head:pull/8245

PR: https://git.openjdk.java.net/jdk/pull/8245