xfrm: interface with if_id 0 should return error

xfrm: interface with if_id 0 should return error

BugLink: https://bugs.launchpad.net/bugs/1959376
[ Upstream commit 8dce43919566f06e865f7e8949f5c10d8c2493f5 ]

xfrm interface if_id = 0 would cause xfrm policy lookup errors since
Commit 9f8550e4bd9d.

Now explicitly fail to create an xfrm interface when if_id = 0

With this commit:
 ip link add ipsec0  type xfrm dev lo  if_id 0
 Error: if_id must be non zero.

v1->v2 change:
 - add Fixes: tag

Fixes: 9f8550e4bd9d ("xfrm: fix disable_xfrm sysctl when used on xfrm interfaces")
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Reviewed-by: Eyal Birger <eyal.birger@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>