test-ls.sh: don't check the symlink file size on NetBSD for now.

NetBSD appears to be returning varying file sizes for symlinks at the
moment, so just ignore the size there for now.

Thanks to Thomas Klausner <tk@giga.or.at> for reporting the problem
and to him and Greg Troxel <gdt@ir.bbn.com> for help with the
workaround.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>