network: add ModemManager support

[Match]
Name=wwan*

[Network]
LLDP=no
LinkLocalAddressing=no
IPv6AcceptRA=no

[ModemManager]
SimpleConnectPropertie]s=apn=internet ip-type=ipv4 allow-roaming=no pin=1111 operator-id=25503
RouteMetric=200
UseGateway=yes

Co-authored-by: Yu Watanabe <watanabe.yu+github@gmail.com>

src/network/networkd-network.c

@@ -512,6 +512,8 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
 
                 .ipoib_mode = _IP_OVER_INFINIBAND_MODE_INVALID,
                 .ipoib_umcast = -1,
+
+                .mm_use_gateway = -1,
         };
 
         r = config_parse_many_full(
@@ -551,6 +553,7 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                         "LLDP\0"
                         "TrafficControlQueueingDiscipline\0"
                         "CAN\0"
+                        "ModemManager\0"
                         "QDisc\0"
                         "BFIFO\0"
                         "CAKE\0"
@@ -847,6 +850,9 @@ static Network *network_free(Network *network) {
         hashmap_free(network->qdiscs_by_section);
         hashmap_free(network->tclasses_by_section);
 
+        /* ModemManager */
+        strv_free(network->mm_simple_connect_props);
+
         return mfree(network);
 }