Add possibility to set gateway in --networkmanager mode

src/hostinfo/networkmanager.py

@@ -259,6 +259,13 @@ def configure_networking(connection, interface, settings=None):
             update['ipv4', 'never-default'] = None
             update['ipv6', 'never-default'] = None
             pass
+        ipv4gw = list(filter(None, [ ip.gateway[0] for ip in interface._ip_]))
+        if ipv4gw:
+            if len(ipv4gw) != 1:
+                raise Exception('Only one gateway allowed')
+            update['ipv4', 'gateway'] = ipv4gw[0]
+            update['ipv4', 'never-default'] = None
+            pass
         ipv6gw = list(filter(None, [ ip.gateway[0] for ip in interface._ipv6_]))
         if ipv6gw:
             if len(ipv6gw) != 1: