meta-google: gbmc-ncsi-config: DHCP impersonation disable

We have platforms that should never impersonate the host DHCP as it
would override perfectly valid IP address configuration on the BMC.
These are newer platforms that guarantee the BMC has a unique address.

Change-Id: I6040f6602cb582793c932878078e3669cba04305
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb b/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
index 217a932..9a2179f 100644
--- a/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
+++ b/meta-google/recipes-google/ncsi/gbmc-ncsi-config.bb
@@ -8,6 +8,7 @@
 GBMC_NCSI_DHCP_RELAY ??= "${@'' if int(d.getVar('FLASH_SIZE')) < 65536 else '1'}"
 GBMC_NCSI_IF_OLD ??= ""
 GBMC_NCSI_PURGE_ETC ??= ""
+GBMC_NCSI_DHCP_IMPERSONATE_HOST ??= "1"
 
 SRC_URI += " \
   ${@'' if d.getVar('GBMC_NCSI_DHCP_RELAY') != '1' else 'file://-bmc-gbmcbrncsidhcp.netdev'} \
@@ -162,6 +163,11 @@
     ${WORKDIR}/gbmc-ncsi-smartnic-wa.sh.in >${WORKDIR}/gbmc-ncsi-smartnic-wa.sh
   install -d -m0755 ${D}${bindir}
   install -m0755 ${WORKDIR}/gbmc-ncsi-smartnic-wa.sh ${D}${bindir}/
+
+  if [ '${GBMC_NCSI_DHCP_IMPERSONATE_HOST}' != 1 ]; then
+    ln -sv /dev/null ${D}${systemd_system_unitdir}/dhcp6@.service
+    ln -sv /dev/null ${D}${systemd_system_unitdir}/dhcp4@.service
+  fi
 }
 
 do_rm_work:prepend() {