Enhance DHCP beyond just OFF and IPv4/IPv6 enabled

Reverting the revert of the revert of commit 2d3b637.
The commits that depend upon this D-Bus change are ready to be
merged.

https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-host-ipmid/+/27278
https://gerrit.openbmc-project.xyz/c/openbmc/phosphor-networkd/+/24666

BMCWeb is using the D-Bus elements provided by this commit.

Change-Id: I53248fe57904afd03d99247a577d892dc53cb2c3
Signed-off-by: Johnathan Mantey <johnathanx.mantey@intel.com>
diff --git a/xyz/openbmc_project/Network/EthernetInterface.interface.yaml b/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
index b18f6c7..9d7dfe6 100644
--- a/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
+++ b/xyz/openbmc_project/Network/EthernetInterface.interface.yaml
@@ -23,7 +23,7 @@
       description: >
           Domain names of the ethernet interface.
     - name: DHCPEnabled
-      type: boolean
+      type: enum[self.DHCPConf]
       description: >
           Address mode of the ethernet interface.
     - name: Nameservers
@@ -83,3 +83,11 @@
         - name: v6
         - name: none
 
+    - name: DHCPConf
+      description: >
+          A list of the permitted DHCP settings used by systemd.
+      values:
+        - name: both
+        - name: v4
+        - name: v6
+        - name: none