Import a patch from debian [1] to fix an issue in dhcp-relay that causes DHCP relay agent does not listen properly for return packets. More information can be found at [2], [3] and [4].
[1] http://anonscm.debian.org/cgit/pkg-dhcp/isc-dhcp.git/tree/debian/patches/dhcrelay-listen.patch
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=648401
[3] https://forum.pfsense.org/index.php?topic=110901.0
[4] https://redmine.pfsense.org/issues/6355
MFH: 2016Q3
Sponsored by: Rubicon Communications (Netgate)