IB/core: Use rdma_read_gid_l2_fields to compare GID L2 fields

Current code tries to derive VLAN ID and compares it with GID
attribute for matching entry. This raw search fails on macvlan
netdevice as its not a VLAN device, but its an upper device of a VLAN
netdevice.

Due to this limitation, incoming QP1 packets fail to match in the
GID table. Such packets are dropped.

Hence, to support it, use the existing rdma_read_gid_l2_fields()
that takes care of diffferent device types.

Fixes: dbf727d ("IB/core: Use GID table in AH creation and dmac resolution")
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Link: https://lore.kernel.org/r/20191002121750.17313-1-leon@kernel.org
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/core/verbs.c

@@ -662,16 +662,17 @@ static bool find_gid_index(const union ib_gid *gid,
 			   void *context)
 {
 	struct find_gid_index_context *ctx = context;
+	u16 vlan_id = 0xffff;
+	int ret;
 
 	if (ctx->gid_type != gid_attr->gid_type)
 		return false;
 
-	if ((!!(ctx->vlan_id != 0xffff) == !is_vlan_dev(gid_attr->ndev)) ||
-	    (is_vlan_dev(gid_attr->ndev) &&
-	     vlan_dev_vlan_id(gid_attr->ndev) != ctx->vlan_id))
+	ret = rdma_read_gid_l2_fields(gid_attr, &vlan_id, NULL);
+	if (ret)
 		return false;
 
-	return true;
+	return ctx->vlan_id == vlan_id;
 }
 
 static const struct ib_gid_attr *