Bluetooth: BR/EDR: Move up code in conn.c

Moves up and consolidate the BREDR specific code to skip certain forward
declaration and to prepare for possibility to initiate authentication
using start_security() routine.

Change-Id: Ic32d7d1376173d47b0eb0481eff37c6e56f995d4
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>