msm: ipa3: add lock for num_q6_rule

There is a race condition be observed
on global variable num_q6_rule used in
ipa wan driver. The fix is to add lock
to prevent different threads are accessing
it at the same time.

Change-Id: Ia9190c60361cb5605b61963309beca3acdeac89d
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>