soc: qcom: wda: Additional cleanup logic

Perform cleanup of WDA and DFC structures when all rmnet VNDs
are removed. This is needed in case IPA notifier callback is
not invoked in for example shutdown process. Also protect the
rmnet check stats function with RCU lock.

Change-Id: I88f0fb7efb73465b467ef37f5dd15a389ee50d1c
Acked-by: Weiyi Chen <weiyic@qti.qualcomm.com>
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>