mem: check mmap failure

If mmap fails, it will return the value MAP_FAILED. Checking for this
return code allows us to properly identify mmap failures and report
them as such to the calling function.

Signed-off-by: Seth Howell <seth.howell@intel.com>
Acked-by: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>

lib/librte_eal/linuxapp/eal/eal_memory.c

@@ -685,6 +685,8 @@ create_shared_memory(const char *filename, const size_t mem_size)
 	}
 	retval = mmap(NULL, mem_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	close(fd);
+	if (retval == MAP_FAILED)
+		return NULL;
 	return retval;
 }