ixgbe: fix X550 DCB

ixgbe: fix X550 DCB

There's a DCB issue on x550. For 8 TCs, if a packet with user priority 6
or 7 is injected to the NIC, then the NIC will put 3 packets into the
queue. There's also a similar issue for 4 TCs.
The root cause is RXPBSIZE is not right. RXPBSIZE of x550 is 384. It's
different from other 10G NICs. We need to set the RXPBSIZE according to
the NIC type.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>