Fix #3700 and other syntax issues:

- Remove -G parameter from pfctl since it doesn't exist anymore
- Initialize $old_router
- Fix sh syntax on variable assign, it couldn't have space before =
- Simplify logic
- Avoid flush states twice, if it was done on IP change, don't do it
  again if router also has changed
Be more precise to match members of a bridge interface, it should fix #3637
remove extra .
Merge branch 'master' of https://github.com/pfsense/pfsense