netlink: consistently use NLA_POLICY_MIN_LEN()

Change places that open-code NLA_POLICY_MIN_LEN() to
use the macro instead, giving us flexibility in how we
handle the details of the macro.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/macsec.c b/drivers/net/macsec.c
index 9159846..124045c 100644
--- a/drivers/net/macsec.c
+++ b/drivers/net/macsec.c
@@ -1611,7 +1611,7 @@ static const struct nla_policy macsec_genl_rxsc_policy[NUM_MACSEC_RXSC_ATTR] = {
 static const struct nla_policy macsec_genl_sa_policy[NUM_MACSEC_SA_ATTR] = {
 	[MACSEC_SA_ATTR_AN] = { .type = NLA_U8 },
 	[MACSEC_SA_ATTR_ACTIVE] = { .type = NLA_U8 },
-	[MACSEC_SA_ATTR_PN] = { .type = NLA_MIN_LEN, .len = 4 },
+	[MACSEC_SA_ATTR_PN] = NLA_POLICY_MIN_LEN(4),
 	[MACSEC_SA_ATTR_KEYID] = { .type = NLA_BINARY,
 				   .len = MACSEC_KEYID_LEN, },
 	[MACSEC_SA_ATTR_KEY] = { .type = NLA_BINARY,