drivers: rmnet_perf: Drop non-IP packets

The legacy behavior of rmnet_perf was to silently drop any non-IP packets
encountered during deaggregation. This patch restores that behavior and
discards all non-IP packets in both the legacy and frag_descriptor paths.
The number of packets dropped in such a manner is tracked via a new module
stat: rmnet_perf_core_non_ip.

Change-Id: Iabc2fe3f0943ffb6300e45ceafb021b7f75e61ec
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>