netdev-dpdk.c: Add generic policer functions.

netdev-dpdk.c: Add generic policer functions.

Add generic policer functions to avoid code duplication.

Policing can be implemented on both egress and ingress paths.
Currently the QoS egress-policer implementation uses it's own specific run
and packet handle policer functions. This patch makes the policer functions
generic so that they can be used regardless of whether the policer is egress
or ingress by just requiring a pointer to the rte_meter used for policing
to be passed.

Signed-off-by: Ian Stokes <ian.stokes@intel.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>