msm: ipa: rm: enhance inactivity timer logic

The current implementation of IPA RM inactivity timer is to set
or cancel the inactivity timer per TX packet to IPA.
For better performance, instead of canceling the timer, a flag is set
to indicate that timer needs to be set again after expiration.
In this was the setting the inactivity timer happens on control path
every 1 second instead of on data path on each TX packet to IPA.

Change-Id: Ibaf34f3549f63feb3fb7b980d2915e30bb700549
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>