Cache the remote device's service channel.

Bluez Device implementation is such that when a device
is unpaired, we removes the device and hence there is no
way to interact with it unless you pair again. Remote service
channel call is used to get the rfcomm channel number which
will be used in profiles like OPP which don't require pairing.

Change-Id: I868a6cdfdb1b7d3591dd8b66cd0320f41a9c1b92