net: qualcomm: rmnet: mark trailer field endianness

The fields in the checksum trailer structure used for QMAP protocol
RX packets are all big-endian format, so define them that way.

It turns out these fields are never actually used by the RMNet code.
The start offset is always assumed to be zero, and the length is
taken from the other packet headers.  So making these fields
explicitly big endian has no effect on the behavior of the code.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>