qemu-file: Make qemu_file_is_writable() non-static

The QEMUFileStdio code will use qemu_file_is_writable() and will be
moved to a separate file.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/qemu-file.c b/qemu-file.c
index a5bbe7e..c303b61 100644
--- a/qemu-file.c
+++ b/qemu-file.c
@@ -456,7 +456,7 @@
     }
 }
 
-static inline bool qemu_file_is_writable(QEMUFile *f)
+bool qemu_file_is_writable(QEMUFile *f)
 {
     return f->ops->writev_buffer || f->ops->put_buffer;
 }