socket: convert socket functions to file scope (static)

The function names used in socket.c conflict with Samba's
socket functions (samba.git/source4/lib/socket/socket.h). Convert
our functions to file scope as they are anyways not called across
files.

Change-Id: If98ae557d3e2868f257c021b283ede6a5e92de02
BUG: 953694
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5168
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>