Add 'auto_gateway' option

If enabled, a default route will be configured using the default gateway. If disabled,
the default route will be removed.

If this variable is not specified, the role will use the default behavior of the
`network_provider` selected.

Setting this option to `no` is equivalent to:
- `DEFROUTE = no` in initscripts, or
- `ipv4.never-default/ipv6.never-default yes` in nmcli

Signed-off-by: Jack Adolph <jack.adolph@gmail.com>

module_utils/network_lsr/argument_validator.py

@@ -578,6 +578,7 @@ class ArgValidator_DictIP(ArgValidatorDict):
                     nested=ArgValidatorIPAddr("address[?]"),
                     default_value=list,
                 ),
+                ArgValidatorBool("auto_gateway", default_value=None),
                 ArgValidatorList(
                     "route", nested=ArgValidatorIPRoute("route[?]"), default_value=list
                 ),
@@ -611,6 +612,7 @@ class ArgValidator_DictIP(ArgValidatorDict):
                 "gateway6": None,
                 "route_metric6": None,
                 "address": [],
+                "auto_gateway": None,
                 "route": [],
                 "route_append_only": False,
                 "rule_append_only": False,
@@ -665,6 +667,20 @@ class ArgValidator_DictIP(ArgValidatorDict):
                 raise ValidationError(
                     name, "'dhcp4_send_hostname' is only valid if 'dhcp4' is enabled"
                 )
+
+        ipv4_gw_defined = result["gateway4"] is not None
+        ipv6_gw_defined = result["gateway6"] is not None
+        dhcp_enabled = result["dhcp4"] or result["auto6"]
+
+        if result["auto_gateway"] and not (
+            ipv4_gw_defined or ipv6_gw_defined or dhcp_enabled
+        ):
+            raise ValidationError(
+                name,
+                "must define 'gateway4', 'gateway6', or use dhcp "
+                "if 'auto_gateway' is enabled",
+            )
+
         return result