dccp: Policy-based packet dequeueing infrastructure

This patch adds a generic infrastructure for policy-based dequeueing of 
TX packets and provides two policies:
 * a simple FIFO policy (which is the default) and
 * a priority based policy (set via socket options).
Both policies honour the tx_qlen sysctl for the maximum size of the write
queue (can be overridden via socket options). 

The priority policy uses skb->priority internally to assign an u32 priority
identifier, using the same ranking as SO_PRIORITY. The skb->priority field
is set to 0 when the packet leaves DCCP. The priority is supplied as ancillary
data using cmsg(3), the patch also provides the requisite parsing routines.

Signed-off-by: Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
diff --git a/net/dccp/Makefile b/net/dccp/Makefile
index b68440b..0c1c9af 100644
--- a/net/dccp/Makefile
+++ b/net/dccp/Makefile
@@ -1,7 +1,7 @@
 obj-$(CONFIG_IP_DCCP) += dccp.o dccp_ipv4.o
 
 dccp-y := ccid.o feat.o input.o minisocks.o options.o \
-	  output.o proto.o timer.o ackvec.o
+	  qpolicy.o output.o proto.o timer.o ackvec.o
 
 dccp_ipv4-y := ipv4.o