migration: Export fd.c functions in its own file

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/migration/migration.c b/migration/migration.c
index c400388..ec93f7a 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -19,6 +19,7 @@
 #include "qemu/main-loop.h"
 #include "migration/blocker.h"
 #include "exec.h"
+#include "fd.h"
 #include "migration/migration.h"
 #include "savevm.h"
 #include "qemu-file-channel.h"