Handle failure of carrier check in dhcp-all-interfaces.sh

As described in the bug, there are conditions with certain switches
in which the interface is 'admin down'ed during initialization.
Doing a 'cat' on /sys/class/net/<interface>/carrier when it is
'admin down'ed produces an 'Invalid Argument' error and the script
terminates.  What this fix does is ignore failures of the 'cat'
operation (by '|| echo 0') and place the link up inside the retry
loop.

Change-Id: I4f098aa5078b8482681394a3e9a6b17ed4bd4451
Closes-Bug: 1654046

elements/dhcp-all-interfaces/install.d/dhcp-all-interfaces.sh

@@ -38,7 +38,7 @@ function serialize_me() {
 }
 
 function get_if_link() {
-    cat /sys/class/net/${1}/carrier
+    cat /sys/class/net/${1}/carrier || echo 0
 }
 
 function enable_interface() {
@@ -87,11 +87,11 @@ function inspect_interface() {
     elif [ "$mac_addr_type" != "0" ]; then
         echo "Device has generated MAC, skipping."
     else
-        ip link set dev $interface up &>/dev/null
-
         local has_link
         local tries
         for ((tries = 0; tries < 20; tries++)); do
+            # Need to set the link up on each iteration
+            ip link set dev $interface up &>/dev/null
             has_link=$(get_if_link $interface)
             [ "$has_link" == "1" ] && break
             sleep 1