[NETFILTER]: xt_tcpudp: fix double unregistration in error path

"xt_unregister_match(AF_INET, &tcp_matchstruct)" is called twice,
leaving "udp_matchstruct" registered, in case of a failure in the
registration of the udp6 structure.

Signed-off-by: Yuri Gushin <yuri@ecl-labs.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>