REORG/MEDIUM: move protocol->{read,write} to sock_ops

The protocol must not set the read and write callbacks, they're specific
to the socket layer. Move them to sock_ops instead.
diff --git a/src/proto_tcp.c b/src/proto_tcp.c
index 1f0d6dc..f709e73 100644
--- a/src/proto_tcp.c
+++ b/src/proto_tcp.c
@@ -70,8 +70,6 @@
 	.sock_addrlen = sizeof(struct sockaddr_in),
 	.l3_addrlen = 32/8,
 	.accept = &stream_sock_accept,
-	.read = &stream_sock_read,
-	.write = &stream_sock_write,
 	.bind = tcp_bind_listener,
 	.bind_all = tcp_bind_listeners,
 	.unbind_all = unbind_all_listeners,
@@ -90,8 +88,6 @@
 	.sock_addrlen = sizeof(struct sockaddr_in6),
 	.l3_addrlen = 128/8,
 	.accept = &stream_sock_accept,
-	.read = &stream_sock_read,
-	.write = &stream_sock_write,
 	.bind = tcp_bind_listener,
 	.bind_all = tcp_bind_listeners,
 	.unbind_all = unbind_all_listeners,
@@ -446,9 +442,9 @@
 	fdtab[fd].owner = si;
 	fdtab[fd].state = FD_STCONN; /* connection in progress */
 	fdtab[fd].flags = FD_FL_TCP | FD_FL_TCP_NODELAY;
-	fdtab[fd].cb[DIR_RD].f = &stream_sock_read;
+	fdtab[fd].cb[DIR_RD].f = si->sock.read;
 	fdtab[fd].cb[DIR_RD].b = si->ib;
-	fdtab[fd].cb[DIR_WR].f = &stream_sock_write;
+	fdtab[fd].cb[DIR_WR].f = si->sock.write;
 	fdtab[fd].cb[DIR_WR].b = si->ob;
 
 	fdinfo[fd].peeraddr = (struct sockaddr *)&si->addr.to;