msm: ipa: eth: Use a wake lock of 500 ms on device activity

Any time we receive a packet from ethernet client, we need to keep APPS
awake for various user space services to process the packet and send any
responses back. Use a wake lock timer of 500 ms to keep the system awake
when rx activity is discovered between two autosleep attempts.

Change-Id: I587075a8a5351c287f23879dda1ebd558f9aa421
Signed-off-by: Jinesh K. Jayakumar <jineshk@codeaurora.org>