netfilter: nf_ct_tcp, udp: fix compilation with sysctl disabled

This patch fixes the compilation of the TCP and UDP trackers with sysctl
compilation disabled:

net/netfilter/nf_conntrack_proto_udp.c: In function ‘udp_init_net_data’:
net/netfilter/nf_conntrack_proto_udp.c:279:13: error: ‘struct nf_proto_net’ has no member named
 ‘user’
net/netfilter/nf_conntrack_proto_tcp.c:1606:9: error: ‘struct nf_proto_net’ has no member named
 ‘user’
net/netfilter/nf_conntrack_proto_tcp.c:1643:9: error: ‘struct nf_proto_net’ has no member named
 ‘user’

Reported-by: Fengguang Wu <wfg@linux.intel.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>