eal/linux: fix build with glibc < 2.12

The function rte_thread_setname needs glibc 2.12,
otherwise it returns -1 without using any parameter.
The macro RTE_SET_USED avoids an "unused parameter" warning.

Fixes: 3901ed99c2 ("eal: fix thread naming on FreeBSD")

Signed-off-by: Thomas Monjalon <thomas.monjalon@6wind.com>

lib/librte_eal/linuxapp/eal/eal_thread.c

@@ -206,5 +206,7 @@ int rte_thread_setname(pthread_t id, const char *name)
 	ret = pthread_setname_np(id, name);
 #endif
 #endif
+	RTE_SET_USED(id);
+	RTE_SET_USED(name);
 	return ret;
 }