ofa_neutron_agent: Fix _phys_br_block_untranslated_traffic

Install the flow to the correct bridge.

Closes-Bug: 1301142
Change-Id: I2aa7ffd6bb297837a39cdd00794af100bf9ab407
(cherry picked from commit 7f5e7c945821b75bd7321bfd0b0c63f2888ac72e)
Merge "ofa_neutron_agent: Fix _phys_br_block_untranslated_traffic" into stable/icehouse