msm: ipa: support aggregated ipa stats query

add support on wan-driver to query modem or
wlan-fw to get the total data usage for all
tethered clients.

Change-Id: I56f40f1c0f6b2ec4279e78b3aeb81c687d08bf2e
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>