net: ipa: specify RX aggregation time limit in config data

Don't assume that a 500 microsecond time limit should be used for
all receive endpoints that support aggregation.  Instead, specify
the time limit to use in the configuration data.

Set a 500 microsecond limit for all existing RX endpoints, as before.

Checking for overflow for the time limit field is a bit complicated.
Rather than duplicate a lot of code in ipa_endpoint_data_valid_one(),
call WARN() if any value is found to be too large when encoding it.

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