msm: ipa: eth: Register interface properties when offload is started

IPA downlink filter rules can get installed during an ethernet link up
event even though the offload path is stopped if we keep the interface
properties registered, leading to data stalls. Register interface with
IPA driver and send offload event to userspace when offload is started.

Change-Id: I202ff0ea863d62be89fdc7b30b480044c7b61931
Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>