xfrm: check id proto in validate_tmpl()

syzbot reported a kernel warning in xfrm_state_fini(), which
indicates that we have entries left in the list
net->xfrm.state_all whose proto is zero. And
xfrm_id_proto_match() doesn't consider them as a match with
IPSEC_PROTO_ANY in this case.

Proto with value 0 is probably not a valid value, at least
verify_newsa_info() doesn't consider it valid either.

This patch fixes it by checking the proto value in
validate_tmpl() and rejecting invalid ones, like what iproute2
does in xfrm_xfrmproto_getbyname().

Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>