(Solaris) return ENOTSUP on unix.Openat error (#68)

xattr_solaris.go

diff --git a/xattr_solaris.go b/xattr_solaris.go
index 38d88d6..8d65b8d 100644
--- a/xattr_solaris.go
+++ b/xattr_solaris.go
@@ -131,7 +131,7 @@
 func flistxattr(f *os.File, data []byte) (int, error) {
 	fd, err := unix.Openat(int(f.Fd()), ".", unix.O_RDONLY|unix.O_XATTR, 0)
 	if err != nil {
-		return 0, err
+		return 0, unix.ENOTSUP
 	}
 	xf := os.NewFile(uintptr(fd), f.Name())
 	defer func() {