Extend gmock to turn off socket listener

Extend gmock to turn off socket listener

On Linux, you'd generally expect this feature to work, but on Cray the
linker warns that the use of getaddrinfo() would require linking a
shared library at runtime. That never happens because we don't use the
socket listener feature, but we don't want people stressing over that
at build time.

Change-Id: I9c358a2923d7563809d471f2ea1767cf2e8bbe25