net: ipa: rework how HOL_BLOCK handling is specified

The head-of-line block (HOLB) drop timer is only meaningful when
dropping packets due to blocking is enabled.  Given that, redefine
the interface so the timer is specified when enabling HOLB drop, and
use a different function when disabling.

To enable and disable HOLB drop, these functions will now be used:
  ipa_endpoint_init_hol_block_enable(endpoint, milliseconds)
  ipa_endpoint_init_hol_block_disable(endpoint)

The existing ipa_endpoint_init_hol_block_enable() becomes a helper
function, renamed ipa_endpoint_init_hol_block_en(), and used with
ipa_endpoint_init_hol_block_timer() to enable HOLB block on an
endpoint.

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