vpe: convert DPKD_PORT to LINK ID

vpe: convert DPKD_PORT to LINK ID

http://dpdk.org/doc/guides/sample_app_ug/ip_pipeline.html#application-resources-present-in-the-configuration-file

LINK instances are created implicitly based on the PORT_MASK application startup
argument. LINK0 is the first port enabled in the PORT_MASK, port 1 is the next one,
etc. The LINK ID is different than the DPDK PMD-level NIC port ID, which is the actual
 position in the bitmask mentioned above. For example, if bit 5 is the first bit set
in the bitmask, then LINK0 is having the PMD ID of 5. This mechanism creates a
contiguous LINK ID space and isolates the configuration file against changes in the
board PCIe slots where NICs are plugged in.

Change-Id: I6e449272cfcfb2b2a75c246f7f569e3f923da245
Signed-off-by: Ross Brattain <ross.b.brattain@intel.com>