iptables: fix compilation when lib[mnl|nftables] are not in standard path

There was several problems:
 a typo in the configure option
 a typo in CFLAGS addon for libmnl and libnftables
 paths to lib were missing on link

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
2 files changed