[bt][rfcomm] Open RFCOMM channels

RFCOMM opens both incoming and outgoing channels.

NET-1013 #done
TEST=bt-host-unittests --gtest_filter='RFCOMM_ChannelManagerTest.Open*'

Change-Id: I6ef1babb03e6cf9b9a08b2fef4cf2ad62c85deb7
5 files changed