ixgbe: Identify FCoE rings earlier to resolve memory corruption w/ FCoE

This patch makes it so that we identify FCoE rings earlier than
ixgbe_set_rx_buffer_len.  Instead we identify the Rx FCoE rings at
allocation time in ixgbe_alloc_q_vector.

The motivation behind this change is to avoid memory corruption when FCoE
is enabled.  Without this change we were initializing the rings at 0, and
2K on systems with 4K pages, then when we bumped the buffer size to 4K with
order 1 pages we were accessing offsets 2K and 6K instead of 0 and 4K.
This was resulting in memory corruptions.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Yi Zou <yi.zou@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>