ixgbevf: Prevent RX/TX statistics getting reset to zero

ixgbevf: Prevent RX/TX statistics getting reset to zero

The commit 4197aa7bb81877ebb06e4f2cc1b5fea2da23a7bd implements 64 bit
per ring statistics. But the driver resets the 'total_bytes' and
'total_packets' from RX and TX rings in the RX and TX interrupt
handlers to zero. This results in statistics being lost and user space
reporting RX and TX statistics as zero. This patch addresses the
issue by preventing the resetting of RX and TX ring statistics to
zero.

Signed-off-by: Narendra K <narendra_k@dell.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>