networkd: Static neighbor support

When using networkd we currently have no way of ensuring that static
neighbor entries are set when our link comes up. This change adds a new
section to the network definition that allows multiple static neighbors
to be set on a link.

test/fuzz/fuzz-network-parser/25-neighbor-section.network

@@ -0,0 +1,6 @@
+[Match]
+Name=dummy98
+
+[Neighbor]
+Address=2004:da8:1:0::
+MACAddress=00:00:5e:00:02:00

test/fuzz/fuzz-network-parser/directives.network

@@ -165,6 +165,9 @@ EmitDNS=
 EmitDomains=
 Managed=
 OtherInformation=
+[Neighbor]
+Address=
+MacAddress=
 [IPv6AddressLabel]
 Label=
 Prefix=

test/test-network/conf/25-neighbor-section.network

@@ -0,0 +1,10 @@
+[Match]
+Name=dummy98
+
+[Neighbor]
+Address=192.168.10.1
+MACAddress=00:00:5e:00:02:65
+
+[Neighbor]
+Address=2004:da8:1:0::1
+MACAddress=00:00:5e:00:02:66

test/test-network/systemd-networkd-tests.py

@@ -525,6 +525,7 @@ class NetworkdNetWorkTests(unittest.TestCase, Utilities):
         '25-fibrule-invert.network',
         '25-fibrule-port-range.network',
         '25-ipv6-address-label-section.network',
+        '25-neighbor-section.network',
         '25-link-section-unmanaged.network',
         '25-route-gateway.network',
         '25-route-gateway-on-link.network',
@@ -775,6 +776,17 @@ class NetworkdNetWorkTests(unittest.TestCase, Utilities):
         print(output)
         self.assertRegex(output, '2004:da8:1::/64')
 
+    def test_ipv6_neighbor(self):
+        self.copy_unit_to_networkd_unit_path('25-neighbor-section.network', '12-dummy.netdev')
+        self.start_networkd()
+
+        self.assertTrue(self.link_exits('dummy98'))
+
+        output = subprocess.check_output(['ip', 'neigh', 'list']).rstrip().decode('utf-8')
+        print(output)
+        self.assertRegex(output, '192.168.10.1.*00:00:5e:00:02:65.*PERMANENT')
+        self.assertRegex(output, '2004:da8:1:0::1.*00:00:5e:00:02:66.*PERMANENT')
+
     def test_sysctl(self):
         self.copy_unit_to_networkd_unit_path('25-sysctl.network', '12-dummy.netdev')
         self.start_networkd()