if_bridge: add ALTQ support
Similar to the recent addition of ALTQ support to if_vlan.
Reviewed by: donner
Obtained from: pfsense
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D31675
(cherry picked from commit eb680a63de1dbf5c974f483975dcb2c60ec6fa08)