rtnetlink: fix error code in rtnl_newlink()

If rtnl_get_peer_net() fails, then propagate the error code.  Don't
return success.

Fixes: 48327566 ("rtnetlink: fix double call of rtnl_link_get_net_ifla()")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/a2d20cd4-387a-4475-887c-bb7d0e88e25a@stanley.mountain


Signed-off-by: Jakub Kicinski <kuba@kernel.org>