drivers: rmnet_perf: Set hash on coalesced descriptors

Although the packet hash value was calculated by rmnet_perf for all
incoming TCP/UDP descriptors, the hash value would not be copied into the
descriptor metadata. Thus, the resulting SKB would not have the hash value
set. This can cause packets in the same flow to be routed to different
cores by rmnet_shs due to the different hash values.

Change-Id: I27fcbb60dc85f66dd439cbf4d0fba3c5c02a3f08
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>