Fix build with GCC 15+ and DPDK 25.11+

GCC 15 introduces __STDC_EMBED_EMPTY__, __STDC_EMBED_FOUND__, and
__STDC_EMBED_NOT_FOUND__ as built-in macros (C23 #embed). These are
dumped into filtered_predefined_macros.h by kern.pre.mk but not
filtered, causing -Werror redefinition errors. Add them to
IMACROS_FILTER.

DPDK 25.11 marks rte_eth_link_get_nowait() with warn_unused_result.
Check the return value in check_all_ports_link_status() to fix the
-Werror build failure.

Author: tarun-t

lib/ff_dpdk_if.c

@@ -217,7 +217,8 @@ check_all_ports_link_status(void)
         for (i = 0; i < nb_ports; i++) {
             uint16_t portid = ff_global_cfg.dpdk.portid_list[i];
             memset(&link, 0, sizeof(link));
-            rte_eth_link_get_nowait(portid, &link);
+            if (rte_eth_link_get_nowait(portid, &link) < 0)
+                link.link_status = 0;
 
             /* print link status if flag set */
             if (print_flag == 1) {

mk/kern.pre.mk

@@ -109,6 +109,7 @@ IMACROS_FILTER+= __CYGWIN__ __CYGWIN32__
 IMACROS_FILTER+= __FreeBSD__
 IMACROS_FILTER+= __linux __linux__ __gnu__linux__ linux
 IMACROS_FILTER+= _WIN32 _WIN64
+IMACROS_FILTER+= __STDC_EMBED_EMPTY__ __STDC_EMBED_FOUND__ __STDC_EMBED_NOT_FOUND__
 
 SPACE= $(eval) $(eval)
 IMACROS_FILTER_EXPR:= $(subst ${SPACE},|,$(strip ${IMACROS_FILTER}))