MEDIUM: protocol: add a pointer to struct sock_ops to the listener struct

The listener struct is now aware of the socket layer to use upon accept().
At the moment, only sock_raw is supported so this patch should not change
anything.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index b3ae050..5bd2cfc 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -265,6 +265,7 @@
 
 			l->fd = -1;
 			l->addr = ss;
+			l->sock = &sock_raw;
 			l->state = LI_INIT;
 
 			if (ss.ss_family == AF_INET) {