selinux: fix a 0/NULL mistmatch in ad_net_init_from_iif()

Use a NULL instead of a zero to resolve a int/pointer mismatch.

Cc: Paolo Abeni <pabeni@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202307210332.4AqFZfzI-lkp@intel.com/
Fixes: dd51fcd4 ("selinux: introduce and use lsm_ad_net_init*() helpers")
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -246,7 +246,7 @@ static void ad_net_init_from_iif(struct common_audit_data *ad,
 				 struct lsm_network_audit *net,
 				 int ifindex, u16 family)
 {
-	__ad_net_init(ad, net, ifindex, 0, family);
+	__ad_net_init(ad, net, ifindex, NULL, family);
 }
 
 /*