port: add pcap file dump

port: add pcap file dump

Originally, sink ports in librte_port releases received mbufs back to
mempool. This patch adds optional packet dumping to PCAP feature in sink
port: the packets will be dumped to user defined PCAP file for storage or
debugging. The user may also choose the sink port's activity: either it
continuously dump the packets to the file, or stops at certain dumping

This feature shares same CONFIG_RTE_PORT_PCAP compiler option as source
port PCAP file support feature. Users can enable or disable this feature
by setting CONFIG_RTE_PORT_PCAP compiler option "y" or "n".

Signed-off-by: Fan Zhang <roy.fan.zhang@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>