netfilter: nft_nat: NFTA_NAT_REG_ADDR_MAX depends on NFTA_NAT_REG_ADDR_MIN

Interpret NFTA_NAT_REG_ADDR_MAX if NFTA_NAT_REG_ADDR_MIN is present,
otherwise, skip it. Same thing with NFTA_NAT_REG_PROTO_MAX.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>