RFR[8u]: 8251546: 8u backport of JDK-8194298 breaks AIX and Solaris builds

[Severin Gehwolf]

Hi,

Could I please get a review of this 8u-only change fixing a build break
on AIX and Solaris introduced with the backport of JDK-8194298? The fix
as such is 8u only as later backports don't have that issue.

The gist of the patch is to:
 * move the impls of {s,g}etTcpSocketOption and socketOptionSupported
   functions out of the else block of ifdef __solaris__. They are
   guarded by their own ifdefs and no-op impls are being provided for
   platforms which aren't supported (as before).
 * define some constants on AIX/Solaris so that the code compiles.
   Constants aren't used in the impl and this allows
   for setTcpSocketOption/getTcpSocketOption call-sites to remain
   outside any ifdef blocks.

Bug: https://bugs.openjdk.java.net/browse/JDK-8251546
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8251546/02/webrev/

Testing: Builds on AIX and Solaris. Linux x86_64 and keepalive tests.

Thoughts?

Thanks,
Severin