net: move random_port() to dns

The random_port() routine is not used anywhere else. Make it local to
dns.c to reduce code clutter, and shrink generated code a little.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
diff --git a/net/dns.c b/net/dns.c
index e35c4dc..5b1fe5b 100644
--- a/net/dns.c
+++ b/net/dns.c
@@ -36,6 +36,16 @@
 
 static int dns_our_port;
 
+/*
+ * make port a little random (1024-17407)
+ * This keeps the math somewhat trivial to compute, and seems to work with
+ * all supported protocols/clients/servers
+ */
+static unsigned int random_port(void)
+{
+	return 1024 + (get_timer(0) % 0x4000);
+}
+
 static void dns_send(void)
 {
 	struct header *header;