whonix_gateway/usr/bin/whonix_firewall: Fix.
When GATEWAY_ALLOW_INCOMING_FLASHPROXY is set to 1, iptables does not support -p all --dport.
See http://serverfault.com/questions/279361/iptables-p-all-dport
Changed to -p tcp, which is sufficient, according to
https://trac.torproject.org/projects/tor/wiki/FlashProxyHowto
Whonix-Gateway firewall: added settings for an optional Tor relay