pipeline: support packet mirroring

pipeline: support packet mirroring

The packet mirroring is configured through slots and sessions, with
the number of slots and sessions set at init.

The new "mirror" instruction assigns one of the existing sessions to a
specific slot, which results in scheduling a mirror operation for the
current packet to be executed later at the time the packet is either
transmitted or dropped.

Several copies of the same input packet can be mirrored to different
output ports by using multiple slots.

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>
Signed-off-by: Kamalakannan R <kamalakannan.r@intel.com>