REORG: listener: move xfer_sock_list to sock.{c,h}.

This will be used for receivers as well thus it is not specific to
listeners but to sockets.
diff --git a/src/haproxy.c b/src/haproxy.c
index 3744547..8381269 100644
--- a/src/haproxy.c
+++ b/src/haproxy.c
@@ -117,6 +117,7 @@
 #include <haproxy/server.h>
 #include <haproxy/session.h>
 #include <haproxy/signal.h>
+#include <haproxy/sock.h>
 #include <haproxy/sock_inet.h>
 #include <haproxy/ssl_sock.h>
 #include <haproxy/stream.h>
diff --git a/src/listener.c b/src/listener.c
index 6e635e3..894c93a 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -44,8 +44,6 @@
 	.list = LIST_HEAD_INIT(bind_keywords.list)
 };
 
-struct xfer_sock_list *xfer_sock_list = NULL;
-
 /* there is one listener queue per thread so that a thread unblocking the
  * global queue can wake up listeners bound only to foreign threads by
  * moving them to the remote queues and waking up the associated tasklet.
diff --git a/src/sock.c b/src/sock.c
index 2eb4b6f..56a4a5c 100644
--- a/src/sock.c
+++ b/src/sock.c
@@ -24,10 +24,13 @@
 
 #include <haproxy/api.h>
 #include <haproxy/connection.h>
+#include <haproxy/listener-t.h>
 #include <haproxy/namespace.h>
 #include <haproxy/sock.h>
 #include <haproxy/tools.h>
 
+/* the list of remaining sockets transferred from an older process */
+struct xfer_sock_list *xfer_sock_list = NULL;
 
 /* Create a socket to connect to the server in conn->dst (which MUST be valid),
  * using the configured namespace if needed, or the one passed by the proxy