pvcalls-front: read all data before closing the connection

pvcalls-front: read all data before closing the connection

[ Upstream commit b79470b64fa9266948d1ce8d825ced94c4f63293 ]

When a connection is closing in_error is set to ENOTCONN. There could
still be outstanding data on the ring left by the backend. Before
closing the connection on the frontend side, drain the ring.

Signed-off-by: Stefano Stabellini <stefanos@xilinx.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>