tcp: Fix listen() regression in 4.19.270

commit fdaf88531cfd17b2a710cceb3141ef6f9085ff40 upstream.

When we backport dadd0dcaa67d ("net/ulp: prevent ULP without clone op from
entering the LISTEN status"), we have accidentally backported a part of
7a7160edf1bf ("net: Return errno in sk->sk_prot->get_port().") and removed
err = -EADDRINUSE in inet_csk_listen_start().

Thus, listen() no longer returns -EADDRINUSE even if ->get_port() failed
as reported in [0].

We set -EADDRINUSE to err just before ->get_port() to fix the regression.

[0]: https://lore.kernel.org/stable/EF8A45D0-768A-4CD5-9A8A-0FA6E610ABF7@winter.cafe/



Reported-by: Winter <winter@winter.cafe>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>