xt_qtaguid: use sock_gen_put() instead of xt_socket_put_sk()

Removing obsolete xt_socket_put_sk() and using sock_gen_put() instead.
xt_socket_put_sk() was reintroduced for xt_qtaguid in one of the patches,
but it turned out sock_gen_put() supersedes xt_socket_put_sk(). So we
don't need xt_socket_put_sk() any more.

This patch is based on commit ID: 1a8bf6ee
"netfilter: xt_socket: use sock_gen_put()"

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: I976d5f7f7eded0f3cc91b596acfeb35e4c2057e5