xfrm: Allow UDP encapsulation only in offload modes

The missing check of x->encap caused to the situation where GSO packets
were created with UDP encapsulation.

As a solution return the encap check for non-offloaded SA.

Fixes: 983a73d ("xfrm: Pass UDP encapsulation in TX packet offload")
Closes: https://lore.kernel.org/all/a650221ae500f0c7cf496c61c96c1b103dcb6f67.camel@redhat.com
Reported-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: rleon

net/xfrm/xfrm_device.c

@@ -407,7 +407,8 @@ bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x)
 	struct xfrm_dst *xdst = (struct xfrm_dst *)dst;
 	struct net_device *dev = x->xso.dev;
 
-	if (!x->type_offload)
+	if (!x->type_offload ||
+	    (x->xso.type == XFRM_DEV_OFFLOAD_UNSPECIFIED && x->encap))
 		return false;
 
 	if (x->xso.type == XFRM_DEV_OFFLOAD_PACKET ||