net/failsafe: support xstats

net/failsafe: support xstats

Add support for extended statistics in failsafe driver.
Reports detailed statistics for each sub device.

Example:

testpmd> show port xstats 1
rx_good_packets: 0
tx_good_packets: 0
rx_good_bytes: 0
tx_good_bytes: 0
rx_missed_errors: 0
rx_errors: 0
tx_errors: 0
rx_mbuf_allocation_errors: 0
rx_q0packets: 0
rx_q0bytes: 0
rx_q0errors: 0
tx_q0packets: 0
tx_q0bytes: 0
rx_sub0_good_packets: 0
tx_sub0_good_packets: 0
...
rx_sub1_good_packets: 0
tx_sub1_good_packets: 0
rx_sub1_good_bytes: 0

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>