Avoid mutex lock wait in socket close failure

Avoid mutex lock wait in socket close failure

In case of absence to close a socket fd during an exit from
application we try to close the same by traversing the
socket_fds in swrap_destructor. But the early lock taken on
libc_symbol_binding_mutex inside the destructor blocks the
subsequent request for locking the same while loading
libc_close within swrap_close.

Also added a test case to verify this flaw in destructor.

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>