net: qualcomm: rmnet: Add support for dowlink marker

The downlink marker command packets provides information
about the total packets which will arrive from the physical
device. Each marker will have information about all the
flows present in the burst regarding the byte and packet
counts.

CRs-Fixed: 2233026
Change-Id: If10394aaa5ed83ea20cb5211d11a47370cc5c41c
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>