Fix compilation of bandwidth-server-many-up.c on FreeBSD

tests/bandwidth-server-many-up.c

@@ -27,6 +27,7 @@
 #if defined(_WIN32)
 #include <ws2tcpip.h>
 #else
+#include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #endif