We compare a payload checksum with a pseudo checksum value for
equality in rmnet_map_ipv4_dl_csum_trailer().  Both of those values
are computed with a unary NOT (~) operation.  The result of the
comparison is the same if we omit that NOT for both values.

Remove these operations in rmnet_map_ipv6_dl_csum_trailer() also.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>