migration/rdma: Fix return-path case

The RDMA code has return-path handling code, but it's only enabled
if postcopy is enabled; if the 'return-path' migration capability
is enabled, the return path is NOT setup but the core migration
code still tries to use it and breaks.

Enable the RDMA return path if either postcopy or the return-path
capability is enabled.

bz: https://bugzilla.redhat.com/show_bug.cgi?id=2063615

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

Author: dagrh

migration/rdma.c

@@ -3373,7 +3373,8 @@ static int qemu_rdma_accept(RDMAContext *rdma)
      * initialize the RDMAContext for return path for postcopy after first
      * connection request reached.
      */
-    if (migrate_postcopy() && !rdma->is_return_path) {
+    if ((migrate_postcopy() || migrate_use_return_path())
+        && !rdma->is_return_path) {
         rdma_return_path = qemu_rdma_data_init(rdma->host_port, NULL);
         if (rdma_return_path == NULL) {
             rdma_ack_cm_event(cm_event);
@@ -3455,7 +3456,8 @@ static int qemu_rdma_accept(RDMAContext *rdma)
     }
 
     /* Accept the second connection request for return path */
-    if (migrate_postcopy() && !rdma->is_return_path) {
+    if ((migrate_postcopy() || migrate_use_return_path())
+        && !rdma->is_return_path) {
         qemu_set_fd_handler(rdma->channel->fd, rdma_accept_incoming_migration,
                             NULL,
                             (void *)(intptr_t)rdma->return_path);
@@ -4192,7 +4194,7 @@ void rdma_start_outgoing_migration(void *opaque,
     }
 
     /* RDMA postcopy need a separate queue pair for return path */
-    if (migrate_postcopy()) {
+    if (migrate_postcopy() || migrate_use_return_path()) {
         rdma_return_path = qemu_rdma_data_init(host_port, errp);
 
         if (rdma_return_path == NULL) {