XHTML Compliance

Firewall - Traffic Shaper
Merge pull request #990 from N0YB/RELENG_2_1

XHTML Compliance
Fix typo on var name
Remove broken 'dynamic6' gateway, we already have ipprotocol to tell us the IP version, leave it more simple using only 'dynamic'. It helps #3484
Validate if src OR dst have IP address set when protocol is IPv4+v6. Fixes #3499
s/unlink/unlink_if_exists/