msm: ipa3: Fix RNDIS Tethering Stats update for UDP UL

Add the tx packet and bytes correctly to the total instead
of resetting it every time for wlan UL stats.

Change-Id: I4316485277351357f08b7241d53b732b74ca6073
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>