spec/ruby/library/socket/*: more FreeBSD fixes

FreeBSD portability notes:

Loopback connections are not instantaneous (unlike Linux), so
non-blocking read-after-write MUST check for readability via
IO.select or IO#wait_readable before attempting non-blocking
recv/read operations.

IPv6 seems favored, so we'll get "::" instead of "0.0.0.0"

Some constants are different or obsolete, so that should be
self-explanatory.

There are still other failures I or somebody else needs to get
to when we have time and feel like dealing with spec DSL:

      http://rubyci.s3.amazonaws.com/freebsd11zfs/ruby-trunk/recent.html

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64239 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/library/socket/basicsocket/recvmsg_nonblock_spec.rb

@@ -156,6 +156,7 @@ describe 'BasicSocket#recvmsg_nonblock' do
 
           describe 'the returned Array' do
             before do
+              platform_is(:freebsd) { IO.select([@socket]) }
               @array = @socket.recvmsg_nonblock
             end