Throw error when invalid MAC Address is set

sdbusplus supports errors on properties, so we can now throw
exceptions on such cases as invalid parameters.

Also changed the journal log levels to ERR.

Tested: Built an image and see invalid parameter errors on values
        like garbage MAC addresses and non-admin MAC Addresses.
Change-Id: I69687bbf34fe51f0c812f40dfc99bb88ce141a2f
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/ethernet_interface.hpp b/ethernet_interface.hpp
index 5109e42..caa042e 100644
--- a/ethernet_interface.hpp
+++ b/ethernet_interface.hpp
@@ -121,7 +121,7 @@
 
         /** @brief sets the MAC address.
          *  @param[in] value - MAC address which needs to be set on the system.
-         *  @returns macAddress of the interface.
+         *  @returns macAddress of the interface or throws an error.
          */
         std::string mACAddress(std::string value) override;