net/mlx5: E-Switch, return error if encap isn't supported

stable inclusion
form stable-v5.10.82
commit 4b4302a02b7f734260856b9c3607fb78d35ba018
bugzilla: 185877 https://gitee.com/openeuler/kernel/issues/I4QU6V

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b4302a02b7f734260856b9c3607fb78d35ba018

--------------------------------

[ Upstream commit c4c31767 ]

On regular ConnectX HCAs getting encap mode isn't supported when the
E-Switch is in NONE mode. Current code would return no error code when
trying to get encap mode in such case which is wrong.

Fix by returning error value to indicate failure to caller in such case.

Fixes: 8e0aa4bc ("net/mlx5: E-switch, Protect eswitch mode changes")
Signed-off-by: NRaed Salem <raeds@nvidia.com>
Reviewed-by: NMark Bloch <mbloch@nvidia.com>
Reviewed-by: NMaor Dickman <maord@nvidia.com>
Signed-off-by: NSaeed Mahameed <saeedm@nvidia.com>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/net/ethernet/mellanox/mlx5/core/eswitch_offloads.c

@@ -2714,7 +2714,7 @@ int mlx5_devlink_eswitch_encap_mode_get(struct devlink *devlink,
 	*encap = esw->offloads.encap;
 unlock:
 	up_write(&esw->mode_lock);
-	return 0;
+	return err;
 }
 
 static bool