[NETFILTER]: ipt_recent: fix sparse warnings

net/ipv4/netfilter/ipt_recent.c:215:17: warning: symbol 't' shadows an earlier one
net/ipv4/netfilter/ipt_recent.c:179:22: originally declared here
net/ipv4/netfilter/ipt_recent.c:322:13: warning: context imbalance in 'recent_seq_start' - wrong count at exit
net/ipv4/netfilter/ipt_recent.c:354:13: warning: context imbalance in 'recent_seq_stop' - unexpected unlock

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>