net: ipa: disable checksum offload for IPA v4.5+

Checksum offload for IPA v4.5+ is implemented differently, using
"inline" offload (which uses a common header format for both upload
and download offload).

The IPA hardware must be programmed to enable MAP checksum offload,
but the RMNet driver is responsible for interpreting checksum
metadata supplied with messages.

Currently, the RMNet driver does not support inline checksum offload.
This support is imminent, but until it is available, do not allow
newer versions of IPA to specify checksum offload for endpoints.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>