Update to use DPDK v1.7.1

Updated the tree to work with a newer DPDK release.  Tested ```examples/tcp_http_get/webbrowser``` with the following hardware/drivers:

    Network devices using DPDK-compatible driver
    ============================================
    0000:01:00.0 'Ethernet Controller 10-Gigabit X540-AT2' drv=igb_uio unused=
    0000:01:00.1 'Ethernet Controller 10-Gigabit X540-AT2' drv=igb_uio unused=
    0000:05:00.0 'I210 Gigabit Network Connection' drv=igb_uio unused=

Note: in my test environment, I cherry-picked buildrump.sh:107fc448 into the older buildrump.sh:8fa8071c submodule to get things to work with my DHCP server.