net: mctp: test: Use correct skb for route input check

BugLink: https://bugs.launchpad.net/bugs/2084005

[ Upstream commit ce335db0621648472f9bb4b7191eb2e13a5793cf ]

In the MCTP route input test, we're routing one skb, then (when delivery
is expected) checking the resulting routed skb.

However, we're currently checking the original skb length, rather than
the routed skb. Check the routed skb instead; the original will have
been freed at this point.

Fixes: 8892c04907 ("mctp: Add route input to socket tests")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/kernel-janitors/4ad204f0-94cf-46c5-bdab-49592addf315@kili.mountain/
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240816-mctp-kunit-skb-fix-v1-1-3c367ac89c27@codeconstruct.com.au
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

net/mctp/test/route-test.c

@@ -354,7 +354,7 @@ static void mctp_test_route_input_sk(struct kunit *test)
 
 		skb2 = skb_recv_datagram(sock->sk, MSG_DONTWAIT, &rc);
 		KUNIT_EXPECT_NOT_ERR_OR_NULL(test, skb2);
-		KUNIT_EXPECT_EQ(test, skb->len, 1);
+		KUNIT_EXPECT_EQ(test, skb2->len, 1);
 
 		skb_free_datagram(sock->sk, skb2);