Bluetooth: RFCOMM: Rearrange fns to avoid forward declaration

Moves rfcomm_send_disc() and rfcomm_session_disconnect() to call it
while doing timer implementation.

Change-Id: I5805d31fb45181193385f055716c8518d68cc4a1
Signed-off-by: Jaganath Kanakkassery <jaganathx.kanakkassery@intel.com>