ofagent: Enable local arp responder for TYPE_FLAT

handling TYPE_FLAT is particularly useful because,
as stated in README, a flat provider network is
the recommended way to provide public network connectivity
for ofagent.

Related: blueprint ofagent-l2pop
Related: blueprint ofagent-merge-bridges
Change-Id: I4f9145ecb6ade44fc884ce7f8842f5e33385391e
ofagent: Enable local arp responder for TYPE_LOCAL

Related: blueprint ofagent-l2pop
Related: blueprint ofagent-merge-bridges
Change-Id: I838917ffffff8fd52c68b4633bd84dccdfe656de
Merge "ofagent: Enable local arp responder for TYPE_FLAT"
Merge "ofagent: Enable local arp responder for TYPE_LOCAL"