libnetutils: Add synchronization per socket full operation

Take and release mutex between ifc_init() and ifc_close()
calls to prevent global ifc_ctl_sock override.

Bug: 22307208

Change-Id: Iacffd329ce2a51defa550c7e33277332045a7b9b
Signed-off-by: Dmitry Shmidt <dimitrysh@google.com>