policy: whitespace cleanup
connection: check whether a reply exists before freeing it

For KDBUS_RECV_DROP, Walk the list of pending replies and see if the
one attached to this queue item is stil there.  It might have been
removed by an incoming reply, and we currently don't track reply
entries in that direction in order to prevent potentially dangling
pointers.

At least atm, KDBUS_RECV_DROP is considered a rarely used operation, so
we can live with that.
Merge remote-tracking branch 'kdbus/master' into 3.13/kdbus