Bluetooth: Revert to mutexes from RCU list

Usage of RCU list looks not reasonalbe for a number of reasons:
our code sleep and we had to use socket spinlocks. Most parts
of code are updaters thus there is little sense to use RCU.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Reviewed-by: Ulisses Furquim <ulisses@profusion.mobi>
Acked-by: Gustavo F. Padovan <padovan@profusion.mobi>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>