net: qualcomm: rmnet: Move headers to linear SKB section

Coalesced packets will always have the L3 and L4 headers in the linear
portion of the SKB. The network stack will copy the headers to the linear
section when it receives a non-linear SKB anyway, so we don't lose
anything by doing it ourselves in all cases.

Change-Id: I10c9139ff2bef15a433a927b6be4597bea040c69
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>