migration: Create x-multifd-channels parameter

Indicates the number of channels that we will create.  By default we
create 2 channels.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>

--

Catch inconsistent defaults (eric).
Improve comment stating that number of threads is the same than number
of sockets
Use new DEFIN_PROP_*
Rename x-multifd-threads to x-multifd-threads
diff --git a/hmp.c b/hmp.c
index 0fb2bc7..bebe19e 100644
--- a/hmp.c
+++ b/hmp.c
@@ -336,6 +336,9 @@
         monitor_printf(mon, "%s: %s\n",
             MigrationParameter_str(MIGRATION_PARAMETER_BLOCK_INCREMENTAL),
             params->block_incremental ? "on" : "off");
+        monitor_printf(mon, "%s: %" PRId64 "\n",
+            MigrationParameter_str(MIGRATION_PARAMETER_X_MULTIFD_CHANNELS),
+            params->x_multifd_channels);
     }
 
     qapi_free_MigrationParameters(params);
@@ -1621,6 +1624,10 @@
         p->has_block_incremental = true;
         visit_type_bool(v, param, &p->block_incremental, &err);
         break;
+    case MIGRATION_PARAMETER_X_MULTIFD_CHANNELS:
+        p->has_x_multifd_channels = true;
+        visit_type_int(v, param, &p->x_multifd_channels, &err);
+        break;
     default:
         assert(0);
     }