meta-google: gbmc-ncsi-config: Remove override if empty

Currently this will make no difference in configuration, but it will be
useful once we implement our DHCP process and need to contend with
multiple configurations.

Change-Id: Ia93530e67cdb88fcbe90ef2b6dfbd5a239469ff7
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meta-google/recipes-google/ncsi/files/gbmc-ncsi-br-pub-addr.sh.in b/meta-google/recipes-google/ncsi/files/gbmc-ncsi-br-pub-addr.sh.in
index b04f2aa..78af419 100644
--- a/meta-google/recipes-google/ncsi/files/gbmc-ncsi-br-pub-addr.sh.in
+++ b/meta-google/recipes-google/ncsi/files/gbmc-ncsi-br-pub-addr.sh.in
@@ -36,14 +36,14 @@
     done
   fi
 
-  local contents='[Network]'$'\n'
+  local contents=
   if (( ${#pfx_bytes[@]} != 0 )); then
     pfx_bytes[8]=0xfd
     local stateless_pfx="$(ip_bytes_to_str pfx_bytes)"
     pfx_bytes[9]=0x01
     local ncsi_pfx="$(ip_bytes_to_str pfx_bytes)"
-    local here=
-    read -r -d '' here <<EOF
+    read -r -d '' contents <<EOF
+[Network]
 Address=$ncsi_pfx/128
 IPv6PrefixDelegation=yes
 [IPv6PrefixDelegation]
@@ -60,13 +60,16 @@
 Type=unreachable
 Metric=1024
 EOF
-    contents+="$here"$'\n'
   fi
 
   local file
   for file in /run/systemd/network/{00,}-bmc-gbmcbr.network.d/50-public.conf; do
     mkdir -p -m 755 "$(dirname "$file")"
-    printf '%s' "$contents" >"$file"
+    if [ -z "$contents" ]; then
+      rm -f "$file"
+    else
+      printf '%s' "$contents" >"$file"
+    fi
   done
 
   # Ensure that systemd-networkd performs a reconfiguration as it doesn't