Specify format for MAC Address

The MAC address format is not defined which makes it hard for the
consumer to process it. Specfying the format according to popular
MAC address convention.

Signed-off-by: Karthick Sundarrajan <karthick.sundarrajan@intel.com>
Change-Id: If6832e58ba856424d297c3823a44d5ce044837e6
diff --git a/xyz/openbmc_project/Network/MACAddress.interface.yaml b/xyz/openbmc_project/Network/MACAddress.interface.yaml
index df092f2..5c9daa0 100644
--- a/xyz/openbmc_project/Network/MACAddress.interface.yaml
+++ b/xyz/openbmc_project/Network/MACAddress.interface.yaml
@@ -5,7 +5,9 @@
     - name: MACAddress
       type: string
       description: >
-          MAC address of the ethernet interface.
+          MAC address of the ethernet interface in six groups of
+          two hexadecimal digits separated by colons.
+          Example: 01:23:45:67:89:AB
       errors:
         - xyz.openbmc_project.Common.Error.InvalidArgument
         - xyz.openbmc_project.Common.Error.InternalFailure