i40e: prevent changing ITR if adaptive-rx/tx enabled

Currently the driver allows the user to change (or even disable)
interrupt moderation if adaptive-rx/tx is enabled when this should
not be the case.

Adaptive RX/TX will not respect the user's ITR settings so
allowing the user to change it is weird.  This bug would also
allow the user to disable interrupt moderation with adaptive-rx/tx
enabled which doesn't make much sense either.

This patch makes it such that if adaptive-rx/tx is enabled, the user
cannot make any manual adjustments to interrupt moderation.  It also
makes it so that if ITR is disabled but adaptive-rx/tx is then
enabled, ITR will be re-enabled.

Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>