tipc: narrow down interface towards struct tipc_link

We move the definition of struct tipc_link from link.h to link.c in
order to minimize its exposure to the rest of the code.

When needed, we define new functions to make it possible for external
entities to access and set data in the link.

Apart from the above, there are no functional changes.

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/netlink_compat.c b/net/tipc/netlink_compat.c
index acda1ce..2c016fd 100644
--- a/net/tipc/netlink_compat.c
+++ b/net/tipc/netlink_compat.c
@@ -1023,13 +1023,13 @@
 		msg->req_type = TIPC_TLV_LINK_NAME;
 		msg->rep_size = ULTRA_STRING_MAX_LEN;
 		msg->rep_type = TIPC_TLV_ULTRA_STRING;
-		dump.dumpit = tipc_nl_link_dump;
+		dump.dumpit = tipc_nl_node_dump_link;
 		dump.format = tipc_nl_compat_link_stat_dump;
 		return tipc_nl_compat_dumpit(&dump, msg);
 	case TIPC_CMD_GET_LINKS:
 		msg->req_type = TIPC_TLV_NET_ADDR;
 		msg->rep_size = ULTRA_STRING_MAX_LEN;
-		dump.dumpit = tipc_nl_link_dump;
+		dump.dumpit = tipc_nl_node_dump_link;
 		dump.format = tipc_nl_compat_link_dump;
 		return tipc_nl_compat_dumpit(&dump, msg);
 	case TIPC_CMD_SET_LINK_TOL: