netfilter: nft_masq: fix uninitialized range in nft_masq_{ipv4, ipv6}_eval

When transferring from the original range in nf_nat_masquerade_{ipv4,ipv6}()
we copy over values from stack in from min_proto/max_proto due to uninitialized
range variable in both, nft_masq_{ipv4,ipv6}_eval. As we only initialize
flags at this time from nft_masq struct, just zero out the rest.

Fixes: 9ba1f726 ("netfilter: nf_tables: add new nft_masq expression")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>