pktgen: add full reset functionality

While testing pktgen, I found that sometimes my configurations from
previous runs would be left over, particularly when going from a test
with 8 threads down to a test with 4 threads.

This adds new functionality to pktgen where you can call
pgset "reset"

and it will be just like you just insmod'ed pktgen again.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Robert Olsson <robert.olsson@its.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>