Fix Ethernet documentation.

1. Remove incorrect @return tag for void function.
2. Fix build breakage by removing the reference to
   #ETHERNET_SERVICE, which is hidden.

Change-Id: Ia893464bafc8257e48e0bd710d27954b535fcece
(cherry picked from commit ff7e406df8a46256e47fff70abc9116ad3f94c23)
2 files changed