ionic: Make the check for Tx HW timestamping more obvious

Currently the checks are:

[1] unlikely(q->features & IONIC_TXQ_F_HWSTAMP)
[2] !unlikely(q->features & IONIC_TXQ_F_HWSTAMP)

[1] is clear enough, but [2] isn't exactly obvious to the
reader because !unlikely reads as likely. However, that's
not what this means.

[2] means that it's unlikely that the q has
IONIC_TXQ_F_HWSTAMP enabled.

Write an inline helper function to hide the unlikely
optimization to make these checks more readable.

Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Link: https://lore.kernel.org/r/20231204210936.16587-5-shannon.nelson@amd.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>