Sync interface state from VPP to LCP

This is the first in a series of functions that aims to copy forward
interface changes in the VPP dataplane into the linux interfaces.

Capture link state changes (set interface state ...) and apply them
to Linux.

There's an important dissonance here:
- When Linux sets a parent interface up, all children also go up.

ip link set enp66s0f1 down
ip link add link enp66s0f1 name foo type vlan id 1234
ip link set foo down
ip link | grep enp66s0f1
9: enp66s0f1: <BROADCAST,MULTICAST> mtu 9000 qdisc mq state DOWN mode DEFAULT group default qlen 1000
61: foo@enp66s0f1: <BROADCAST,MULTICAST,M-DOWN> mtu 9000 qdisc noop state DOWN mode DEFAULT group default qlen 1000

ip link set enp66s0f1 up
ip link | grep s0f1
9: enp66s0f1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc mq state UP mode DEFAULT group default qlen 1000
61: foo@enp66s0f1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc noqueue state UP mode DEFAULT group default qlen 1000

While in VPP this is not so, there each individual interface and
sub-interface stands for itself. I think the proper fix here is to walk
all sub-interfaces when a phy changes, and force a sync of those from
VPP to LCP as well. I'll do that in a followup commit so it's easier to
roll back.

lcpng_if_sync.c

@@ -0,0 +1,72 @@
+/* Hey Emacs use -*- mode: C -*- */
+/*
+ * Copyright 2021 Pim van Pelt <pim@ipng.nl>
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <sys/socket.h>
+#include <linux/if.h>
+
+#include <vnet/vnet.h>
+#include <vnet/plugin/plugin.h>
+
+#include <plugins/lcpng/lcpng_interface.h>
+
+#include <vlibapi/api.h>
+#include <vlibmemory/api.h>
+#include <vpp/app/version.h>
+#include <vnet/format_fns.h>
+#include <vnet/udp/udp.h>
+#include <vnet/tcp/tcp.h>
+#include <vnet/devices/tap/tap.h>
+#include <vnet/devices/netlink.h>
+
+
+static clib_error_t *
+lcp_itf_admin_state_change (vnet_main_t * vnm, u32 sw_if_index, u32 flags)
+{
+  const lcp_itf_pair_t *lip;
+  vnet_hw_interface_t *hi;
+  vnet_sw_interface_t *si;
+
+  LCP_ITF_PAIR_DBG ("admin_state_change: sw %U %u",
+		  format_vnet_sw_if_index_name, vnm, sw_if_index,
+		  flags);
+
+  // Sync interface state changes into host
+  lip = lcp_itf_pair_get (lcp_itf_pair_find_by_phy (sw_if_index));
+  if (!lip) return NULL;
+
+  LCP_ITF_PAIR_INFO ("admin_state_change: %U flags %u", format_lcp_itf_pair, lip, flags);
+  lcp_itf_set_link_state (lip, (flags & VNET_HW_INTERFACE_FLAG_LINK_UP));
+
+  // Sync PHY carrier changes into TAP
+  hi = vnet_get_hw_interface_or_null (vnm, sw_if_index);
+  si = vnet_get_sw_interface_or_null (vnm, lip->lip_host_sw_if_index);
+  if (!si || !hi) return NULL;
+  LCP_ITF_PAIR_INFO ("admin_state_change: hi %U si %U %u",
+		  format_vnet_sw_if_index_name, vnm, hi->hw_if_index,
+		  format_vnet_sw_if_index_name, vnm, si->sw_if_index,
+		  flags);
+
+  tap_set_carrier (si->hw_if_index, (flags & VNET_HW_INTERFACE_FLAG_LINK_UP));
+  /* TODO(pim): is this right? see tap_set_speed() "Cannot open netns" error
+  if (flags & VNET_HW_INTERFACE_FLAG_LINK_UP) {
+    tap_set_speed (si->hw_if_index, hi->link_speed);
+  } 
+  */
+  return NULL;
+}   
+
+VNET_SW_INTERFACE_ADMIN_UP_DOWN_FUNCTION(lcp_itf_admin_state_change);