net: if: Check IPv4 pointers properly in TTL setters/getters

We must make sure that IPv4 configuration pointer is valid
so that the TTL can be set for a given interface.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>

subsys/net/ip/net_if.c

@@ -3165,6 +3165,10 @@ uint8_t net_if_ipv4_get_ttl(struct net_if *iface)
 
 	net_if_lock(iface);
 
+	if (net_if_config_ipv4_get(iface, NULL) < 0) {
+		goto out;
+	}
+
 	if (!iface->config.ip.ipv4) {
 		goto out;
 	}
@@ -3186,6 +3190,10 @@ void net_if_ipv4_set_ttl(struct net_if *iface, uint8_t ttl)
 #if defined(CONFIG_NET_NATIVE_IPV4)
 	net_if_lock(iface);
 
+	if (net_if_config_ipv4_get(iface, NULL) < 0) {
+		goto out;
+	}
+
 	if (!iface->config.ip.ipv4) {
 		goto out;
 	}
@@ -3206,6 +3214,10 @@ uint8_t net_if_ipv4_get_mcast_ttl(struct net_if *iface)
 
 	net_if_lock(iface);
 
+	if (net_if_config_ipv4_get(iface, NULL) < 0) {
+		goto out;
+	}
+
 	if (!iface->config.ip.ipv4) {
 		goto out;
 	}
@@ -3227,6 +3239,10 @@ void net_if_ipv4_set_mcast_ttl(struct net_if *iface, uint8_t ttl)
 #if defined(CONFIG_NET_NATIVE_IPV4)
 	net_if_lock(iface);
 
+	if (net_if_config_ipv4_get(iface, NULL) < 0) {
+		goto out;
+	}
+
 	if (!iface->config.ip.ipv4) {
 		goto out;
 	}