netfilter: cttimeout: remove set but not used variable 'l3num'

Fixes gcc '-Wunused-but-set-variable' warning:

net/netfilter/nfnetlink_cttimeout.c: In function 'cttimeout_default_set':
net/netfilter/nfnetlink_cttimeout.c:353:8: warning:
variable 'l3num' set but not used [-Wunused-but-set-variable]

It not used any more after
commit dd2934a95701 ("netfilter: conntrack: remove l3->l4 mapping information")

Signed-off-by: YueHaibing <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nfnetlink_cttimeout.c

···
 				 struct netlink_ext_ack *extack)
 {
 	const struct nf_conntrack_l4proto *l4proto;
-	__u16 l3num;
 	__u8 l4num;
 	int ret;
 
···
 	    !cda[CTA_TIMEOUT_DATA])
 		return -EINVAL;
 
-	l3num = ntohs(nla_get_be16(cda[CTA_TIMEOUT_L3PROTO]));
 	l4num = nla_get_u8(cda[CTA_TIMEOUT_L4PROTO]);
 	l4proto = nf_ct_l4proto_find_get(l4num);