Support mounting ext2fs file systems with -async to the small extent

that ext2fs in the kernel supports async mounts.  ext2fs used to
effectively force the -async flag on.  -async for ext2fs only gives
async (more precisely, delayed) writes for inode updates, so it is
barely worth using even when it is safe.

sbin/mount_ext2fs/mount_ext2fs.c

@@ -60,6 +60,7 @@ static const char rcsid[] =
 
 struct mntopt mopts[] = {
 	MOPT_STDOPTS,
+	MOPT_ASYNC,
 	MOPT_FORCE,
 	MOPT_SYNC,
 	MOPT_UPDATE,