app/testpmd: add option to configure UDP tunnel port

app/testpmd: add option to configure UDP tunnel port

This change adds a new option to "port config" command to
add udp tunnel port for VXLAN and GENEVE tunneling protocols.
This command can be extended for other tunneling protocols
listed in "enum rte_eth_tunnel_type" as and when needed.

usage:
port config <port_id> udp_tunnel_port add|rm vxlan|geneve <udp_port>

Signed-off-by: Shahed Shaikh <shahed.shaikh@cavium.com>
Signed-off-by: Rasesh Mody <rasesh.mody@cavium.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>