net: qrtr: Do not take sock lock on blocking recv

Socket client's should be able to block on recv without blocking other
socket operations such as sending. The qrtr core logic should also be
able to operate on the sock while a client is blocked in recv. Remove
the sock lock from around the recv_datagram to allow execution to
continue while a client is blocked in recv.

Change-Id: I6adb09b8e44c5ff3542b88db87b376a3ae5cb5ba
Signed-off-by: Chris Lew <clew@codeaurora.org>