[MEDIUM] Collect & provide separate statistics for sockets, v2

This patch allows to collect & provide separate statistics for each socket.
It can be very useful if you would like to distinguish between traffic
generate by local and remote users or between different types of remote
clients (peerings, domestic, foreign).

Currently no "Session rate" is supported, but adding it should be possible
if we found it useful.
diff --git a/include/proto/dumpstats.h b/include/proto/dumpstats.h
index 700fc95..ea579f5 100644
--- a/include/proto/dumpstats.h
+++ b/include/proto/dumpstats.h
@@ -38,6 +38,7 @@
 #define STATS_TYPE_FE  0
 #define STATS_TYPE_BE  1
 #define STATS_TYPE_SV  2
+#define STATS_TYPE_SO  3
 
 /* unix stats socket states */
 #define STAT_CLI_INIT   0   /* initial state */