configure: Fix DPDK linking when using a relative path

When linking with DPDK, if a relative path is used with the
'--with-dpdk' flag, then OVS will always be compiled with vHost Cuse
support, even if it is not enabled in the DPDK build.
This patch fixes this problem, and enables the correct version of
vHost despite whether or not a relative or absolute path is used.

Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

acinclude.m4

@@ -174,9 +174,10 @@ AC_DEFUN([OVS_CHECK_DPDK], [
     DPDK_LIB_DIR=$RTE_SDK/lib
     DPDK_LIB="-ldpdk"
     DPDK_EXTRA_LIB=""
+    RTE_SDK_FULL=`readlink -f $RTE_SDK`
 
     AC_COMPILE_IFELSE(
-      [AC_LANG_PROGRAM([#include <$RTE_SDK/include/rte_config.h>
+      [AC_LANG_PROGRAM([#include <$RTE_SDK_FULL/include/rte_config.h>
 #if !RTE_LIBRTE_VHOST_USER
 #error
 #endif], [])],