drivers: rmnet_perf: clone UDP SKBs when deaggregating

The base RmNet driver will clone UDP packets of more than 64 bytes
in length instead of allocating new SKBs and copying the data. Mimic
this behavior in the perf module as well.

CRs-Fixed: 2327928
Change-Id: I7e98b50ee0fc2e58285e9758378531be20bef0eb
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>