net: ipa: get rid of some unneeded IPA interrupt code

The pending IPA interrupts are checked by ipa_isr_thread(), and
interrupts are processed only if an enabled interrupt has a
condition pending.  But ipa_interrupt_process_all() now makes the
same check, so the one in ipa_isr_thread() can just be skipped.

Also in ipa_isr_thread(), any interrupt conditions pending which are
not enabled are cleared.  Here too, ipa_interrupt_process_all() now
clears such excess interrupt conditions, so ipa_isr_thread() doesn't
have to.

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