msm: ipa: eth: Use single netdevice notifier registration

Registering with netdevice notifier while holding upper_mutex can
deadlock if an active notification is in parallel waiting for the
same mutex, as the rtnl mutex needed for the registation is held
by the notification handler in this scenario. Re-use the notifier
registration used for real device to also monitor for events from
upper interfaces.

Change-Id: Ia2ef72be4b831077050e18c93781ea620e956820
Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>