net: ipa: reverse logic on escape buffer use

Starting with IPA v4.2 there is a GSI channel option to use an
"escape buffer" instead of prefetch buffers.  This should be used
for all channels *except* the AP command TX channel.  The logic
that implements this has it backwards; fix this bug.

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