net: ipa: more completely check endpoint validity

Ensure all defined TX endpoints are in the range [0, CONS_PIPES) and
defined RX endpoints are within [PROD_LOWEST, PROD_LOWEST+PROD_PIPES).

Modify the way local variables are used to make the checks easier
to understand.  Check for each endpoint being in valid range in the
loop, and drop the logical-AND check of initialized against
unavailable IDs.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>