parser: allow both nat_flags and port specification in redirect

parser: allow both nat_flags and port specification in redirect

This patch changes the parser to permit both nat_flags and port specification
in the redirect expression.

The resulting syntax is:
 % nft add rule nat prerouting redirect [port] [nat_flags]

The port specification requires a bit of context regardin the transport
protocol. Some examples:
 % nft add rule nat prerouting tcp dport 22 redirect :23
 % nft add rule add prerouting udp dport 53 redirect :5353

The nat_flags argument is the last argument:
 % nft add rule nat prerouting tdp dport 80 redirect :8080 random

The port specification can be a range:
 % nft add rule nat prerouting tcp dport 80 redirect :8080-8090 random

While at it, the regression tests files are updated.

Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>