netfilter: optimize nf_inet_addr_cmp

optimize nf_inet_addr_cmp by 64bit xor computation
similar to ipv6_addr_equal()

Signed-off-by: Yuan Linsi <yuanlinsi01@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>