xfrm: fix the if_id check in changelink

stable inclusion
from linux-4.19.233
commit 33c4a43021acfb91e289b2d92e2db0f4a8fcf41e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5646A


CVE: NA

--------------------------------

commit 6d0d95a1 upstream.

if_id will be always 0, because it was not yet initialized.

Fixes: 8dce4391 ("xfrm: interface with if_id 0 should return error")
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>