net: qualcomm: rmnet: Allow to reset rmnet private stats

Use the ethtool private stats handler to reset statistics of
the rmnet private stats.

CRs-Fixed: 2512312
Change-Id: I8337b0d79b1ca2a98cb706e762a3dd7baa386706
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>