migration: clean up server sockets and handlers before invoking process_incoming_migration

A first step towards making a common "suffix" for all migration protocols,
and moving it to process_incoming_migration.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/migration-fd.c b/migration-fd.c
index b47b222..a4cd83f 100644
--- a/migration-fd.c
+++ b/migration-fd.c
@@ -92,8 +92,8 @@
 {
     QEMUFile *f = opaque;
 
-    process_incoming_migration(f);
     qemu_set_fd_handler2(qemu_get_fd(f), NULL, NULL, NULL, NULL);
+    process_incoming_migration(f);
     qemu_fclose(f);
 }