Bluetooth: Refactor handling of identity address lookup

This reduces number of idefs cuts and make code much easier to read.
In case of SMP not supported (or connection support since SMP depends
on it) find_id_addr is simplified and will most likely be inlined by
compiler resulting in no-op.

Change-Id: Ib16d1508c5664fcb58f619b090a5d62b2ecfe8c5
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>