ofagent: bye bye br-tun

WIP

Implements: blueprint ofagent-merge-bridges
Change-Id: I21ee1c6d141863182b487e10c7bfe911b1a472ab
ofa_neutron_agent: l2pop_network_types

Change-Id: I2f200a1ae2bd769ea1f83fe65e58e82325ed92b0