netdev-dpdk: Move to DPDK 1.7.1

This patch updates the documentation to reflect that DPDK 1.7.1
is supported. Travis scripts have also been updated to reflect
this. DPDK phy and ring ports were validated against DPDK 1.7.1.

Reviewed-by: Mark D. Gray <mark.d.gray@intel.com>
Signed-off-by: Maryam Tahhan <maryam.tahhan@intel.com>
Acked-by: Daniele Di Proietto <ddiproietto@vmware.com>
Acked-by: Thomas Graf <tgraf@noironetworks.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
INSTALL.DPDK: improve documentation

Signed-off-by: Daniele Di Proietto <ddiproietto@vmware.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Makefile.am: Properly indent INSTALL.DPDK

Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>