ofagent: Use port desc to monitor ports on br-int

also, use ofport.name as device identifiers.
sprinkle some TODO comments.

Implements: blueprint ofagent-port-monitor
Change-Id: I4995964f37729f954fec71c4a2e61e463a430b1a
Use correct MAX_LEN constant in agent functional tests

Closes-bug: #1334922

Change-Id: I62bd12da21e778f5cca97d6280c107575d912a81
Merge "ofagent: Use port desc to monitor ports on br-int"
Merge "Use correct MAX_LEN constant in agent functional tests"