net: ipa: use Qtime for IPA v4.5 head-of-line time limit

Extend ipa_reg_init_hol_block_timer_val() so it properly calculates
the head-of-line block timeout to use for IPA v4.5.

Introduce hol_block_timer_qtime_val() to compute the value to use
for IPA v4.5, where Qtime is used as the basis of the timer.  Call
that function from hol_block_timer_val() for IPA v4.5.

Both of these are private functions, so shorten their names a bit so
they don't take up so much space on the line.

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