dpdkstat: fix configure.ac and src/Makefile

dpdkstat: fix configure.ac and src/Makefile

Fix configuration.ac and src/Makefile based on comments from pull
request review.
  * Removed unnecessary libs.
  * Removed unnecessary compilation flags.
  * Fixed indentation in configure.ac
  * Remove duplicate AC_CHECK_LIB check.
  * Compare FOUND_DPDK with xtrue explicitly.
  * Change standalone instances of dpdk to libdpdk.
  * Add BUILD_WITH_DPDK_LIBS to dpdkstat_la_LIBADD.

Change-Id: I27b0c888f81cac3219fdc97174e31770dbd5e746
Signed-off-by: Maryam Tahhan <maryam.tahhan@intel.com>