xfrm: restore GSO for SW crypto

Commit 49431af incorrectly assumes that the GSO path is only used
by HW offload, but it's also useful for SW crypto.

This patch re-enables GSO for SW crypto. It's not an exact revert to
preserve the other changes made to xfrm_dev_offload_ok afterwards, but
it reverts all of its effects.

Fixes: 49431af ("xfrm: rely on XFRM offload")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: qsn

net/xfrm/xfrm_device.c

@@ -415,10 +415,12 @@ bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x)
 	struct net_device *dev = x->xso.dev;
 	bool check_tunnel_size;
 
-	if (x->xso.type == XFRM_DEV_OFFLOAD_UNSPECIFIED)
+	if (!x->type_offload ||
+	    (x->xso.type == XFRM_DEV_OFFLOAD_UNSPECIFIED && x->encap))
 		return false;
 
-	if ((dev == xfrm_dst_path(dst)->dev) && !xdst->child->xfrm) {
+	if ((!dev || dev == xfrm_dst_path(dst)->dev) &&
+	    !xdst->child->xfrm) {
 		mtu = xfrm_state_mtu(x, xdst->child_mtu_cached);
 		if (skb->len <= mtu)
 			goto ok;
@@ -430,6 +432,9 @@ bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x)
 	return false;
 
 ok:
+	if (!dev)
+		return true;
+
 	check_tunnel_size = x->xso.type == XFRM_DEV_OFFLOAD_PACKET &&
 			    x->props.mode == XFRM_MODE_TUNNEL;
 	switch (x->props.family) {