i40e: Remove separate functions gathering XOFF Rx stats

The separate functions to gather Flow control Rx XOFF stats was to
determine if the Tx for a queue was paused due to Link Flow Control(LFC)
or Priority Flow Control(PFC).

But, with recent change in the i40e driver the logic for checking th Tx
hang has been removed and these functions don't do anything meaningful.
Hence, there is no need to keep these separate functions to gather Rx
XOFF stats for LFC or PFC.

This patch removes these functions and moves the stat collection for
XOFF Rx to the i40e_update_pf_stats() that collects all the PF stats.

Change-ID: Iec1452dac3a6766f0d968e754cb407530d7c60cd
Signed-off-by: Neerav Parikh <neerav.parikh@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>