Add startup conf options to set per-interface descriptor ring size

Add startup conf options to set per-interface descriptor ring size

This patch introduces following 2 startup options:

  num-rx-desc
  num-tx-desc

Which can be specified under the dpdk { dev PCI_ADDR {...} } or
dpdk { dev default {...} } .

"show hardware" output is extended to display what is set:

TenGigabitEthernet2/0/0            5    down  TenGigabitEthernet2/0/0
  Ethernet address 90:e2:ba:96:d0:54
  Intel 82599
    carrier up full duplex speed 10000 mtu 9216
    rx queues 2, rx desc 512, tx queues 2, tx desc 1024
    cpu socket 0

Change-Id: Ia832885c8e5cf0eb0575367e97581e7065934753
Signed-off-by: Damjan Marion <damarion@cisco.com>