acinclude: Omit unnecessary define

Commit fc3b425 ("acinclude: Include libmnl when needed") added
unnecessary include of DPDK_MNL. Omit it.

Fixes: fc3b425 ("acinclude: Include libmnl when needed")
Signed-off-by: Eli Britstein <elibr@mellanox.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

acinclude.m4

@@ -298,8 +298,7 @@ AC_DEFUN([OVS_CHECK_DPDK], [
 #endif
         ], [])
       ], [],
-      [AC_SEARCH_LIBS([mnl_attr_put],[mnl],[],[AC_MSG_ERROR([unable to find libmnl, install the dependency package])])
-       AC_DEFINE([DPDK_MNL], [1], [MLX5 PMD detected in DPDK.])])
+      [AC_SEARCH_LIBS([mnl_attr_put],[mnl],[],[AC_MSG_ERROR([unable to find libmnl, install the dependency package])])])
 
     AC_COMPILE_IFELSE([
       AC_LANG_PROGRAM(