fix ipv6 compilation under macosx >= 1070 - v3

fix ipv6 compilation under macosx >= 1070 - v3

 - use __APPLE_USE_RFC_3542 for macosx build environment >= 1070
 - define SOL_IP from IPPROTO_IP if it's missing
   In Linux man 7 ip says:
   "Using SOL_IP socket options level isn't portable, BSD-based
   stacks use IPPROTO_IP level."

Signed-off-by: JuanJo Ciarlante <jjo+ml@google.com>
Tested-by: Eric F Crist <ecrist@secure-computing.net>
Acked-by: David Sommerseth <davids@redhat.com>
Signed-off-by: David Sommerseth <davids@redhat.com>