Bluetooth: Introduce a timeout for synchronous HCI command sending

There is no command that should take more than a couple of seconds. If
it does there's something severely wrong with the system. Catch such
situations with a clear assert rather than silently blocking the
sending thread.

Change-Id: Ie981fddcc27059df3e4df586e86ceac2e348f509
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>