xfrm: Allow transport-mode states with AF_UNSPEC selector

xfrm state selectors are matched against the inner-most flow
which can be of any address family.  Therefore middle states
in nested configurations need to carry a wildcard selector in
order to work at all.

However, this is currently forbidden for transport-mode states.

Fix this by removing the unnecessary check.

Fixes: 13996378 ("[IPSEC]: Rename mode to outer_mode and add inner_mode")
Reported-by: NDavid George <David.George@sophos.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NSteffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_state.c

@@ -2815,11 +2815,6 @@ int __xfrm_init_state(struct xfrm_state *x, bool init_replay, bool offload,
 			goto error;
 		}
 
-		if (!(inner_mode->flags & XFRM_MODE_FLAG_TUNNEL)) {
-			NL_SET_ERR_MSG(extack, "Only tunnel modes can accommodate an AF_UNSPEC selector");
-			goto error;
-		}
-
 		x->inner_mode = *inner_mode;
 
 		if (x->props.family == AF_INET)