Fixed long size in UDP port bitmap index

There is issue when you are using 64bit Linux and increasing RT_UDP_SOCKETS
above 64, because on 64 bit Linux long has 64 bits instead of hardcoded 32
bits. This patch fixes the situation on both 32 and 64 bit OS.
Signed-off-by: Matúš Olekšák <oleksak.matus@gmail.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kernel/drivers/net/stack/ipv4/udp/udp.c

@@ -301,7 +301,7 @@ int rt_udp_socket(struct rtdm_fd *fd)
 			break;
 	index = ffz(port_bitmap[i]);
 	set_bit(index, &port_bitmap[i]);
-	index += i * 32;
+	index += i * BITS_PER_LONG;
 	sock->prot.inet.reg_index = index;
 	sock->prot.inet.sport = index + auto_port_start;