[MINOR] proxy: add an accept() callback for the application layer

This will be used by the application layer for setting accept callbacks.
diff --git a/include/types/proxy.h b/include/types/proxy.h
index 0c1ca76..f7d4e8c 100644
--- a/include/types/proxy.h
+++ b/include/types/proxy.h
@@ -257,6 +257,7 @@
 #endif
 	int iface_len;				/* bind interface name length */
 	char *iface_name;			/* bind interface name or NULL */
+	int (*accept)(struct session *s);       /* application layer's accept() */
 	struct proxy *next;
 	struct logsrv logsrv1, logsrv2;		/* 2 syslog servers */
 	signed char logfac1, logfac2;		/* log facility for both servers. -1 = disabled */