net: distribute udp packets according to address pair

net/udp.cc

@@ -98,8 +98,9 @@ unsigned udp_v4::forward(packet& p, size_t off, ipv4_address from, ipv4_address
     }
 
     auto dst = ntoh(uh->dst_port);
+    auto src = ntoh(uh->src_port);
 
-    return dst % smp::count;
+    return connid_hash()(connid{to, from, dst, src}) % smp::count;
 }
 
 void udp_v4::received(packet p, ipv4_address from, ipv4_address to)

net/udp.hh

@@ -41,6 +41,9 @@ struct udp_channel_state {
 };
 
 class udp_v4 : ip_protocol {
+    using connid = l4connid<ipv4_traits>;
+    using connid_hash = typename connid::connid_hash;
+
 public:
     static const int default_queue_size;
 private: