net: sockets: Release the socket lock if needed

If we are waiting all the data i.e., the MSG_WAITALL flag is set,
then if we have not yet received all the data at the end of the
receive loop. We must use the condition variable to get the signal
when the data is ready to be received. Otherwise the receive loop
will not release the socket lock and receive_cb will not be able
to indicate that data is received.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>