coreos-teardown-initramfs-network: simplify networking takedown

On recommendation from the NM team let's try to delete the device
first and if that doesn't work then set it to down and flush any
associated addresses. Deleting virtual devices (bonds, teams, bridges,
ip-tunnels, etc) will clean up any associated kernel resources, so
this makes the logic for bringing down these devices easier. A real
device can't be deleted so that will fail and we'll fallback to setting
it down and flushing addresses.

dracut/30ignition/coreos-teardown-initramfs-network.sh

@@ -32,27 +32,19 @@ propagate_initramfs_networking() {
 
 down_interface() {
     echo "info: taking down network device: $1"
-    ip link set $1 down
-    ip addr flush dev $1
-}
-
-down_teams() {
-    # We think since teaming is mostly achieved in userspace (with a
-    # daemon) we don't think there is anything to do here because the
-    # daemon will get taken down before the switch to the real root.
-}
-
-down_bonds() {
-    if [ -f "/sys/class/net/bonding_masters" ]; then
-        bonds="$(cat /sys/class/net/bonding_masters)"
-        for b in ${bonds[@]}; do
-            down_interface ${b}
-            echo -"${b}" > /sys/class/net/bonding_masters
-         done
+    # On recommendation from the NM team let's try to delete the device
+    # first and if that doesn't work then set it to down and flush any
+    # associated addresses. Deleting virtual devices (bonds, teams, bridges,
+    # ip-tunnels, etc) will clean up any associated kernel resources. A real
+    # device can't be deleted so that will fail and we'll fallback to setting
+    # it down and flushing addresses.
+    if ! ip link delete $1; then
+        ip link set $1 down
+        ip addr flush dev $1
     fi
 }
 
-# This mimics the behaviour of dracut's ifdown() in net-lib.sh
+# Iterate through the interfaces in the machine and take them down.
 # Note that in the futre we would like to possibly use `nmcli` networking off`
 # for this. See the following two comments for details:
 # https://github.com/coreos/fedora-coreos-tracker/issues/394#issuecomment-599721763
@@ -62,19 +54,15 @@ down_interfaces() {
         for f in /sys/class/net/*; do
             interface=$(basename "$f")
             # The `bonding_masters` entry is not a true interface and thus
-            # cannot be taken down.  If they existed, the bonded interfaces
-            # were taken down earlier in this script.
+            # cannot be taken down.
             if [ "$interface" == "bonding_masters" ]; then continue; fi
             down_interface $interface
         done
     fi
 }
 
 main() {
-    # We want to take down the bonds/teams first and then clean
-    # up interfaces set up in the ininitramfs
-    down_bonds
-    down_teams
+    # Take down all interfaces set up in the initramfs
     down_interfaces
 
     # Clean up all routing