af-packet: implement rollover option

af-packet: implement rollover option

This patch implements the rollover option in af_packet capture.
This should heavily minimize the packet drops as well as the
maximum bandwidth treated for a single flow.

The option has been deactivated by default but it is activated in
the af_packet default section. This ensure there is no change for
old users using an existing YAML. And new users will benefit from
the change.

This option is available since Linux 3.10. An analysis of af_packet
kernel code shows that setting the flag in all cases should not
cause any trouble for older kernel.