native: mark internal routines

These (generally) cannot be made unexported because we test via
testlapack.

Also fix a name and some capitalisation.

native/dlae2.go

@@ -11,6 +11,8 @@ import "math"
 //  [b c]
 // and returns the eigenvalue with the larger absolute value as rt1 and the
 // smaller as rt2.
+//
+// Dlae2 is an internal routine. It is exported for testing purposes.
 func (impl Implementation) Dlae2(a, b, c float64) (rt1, rt2 float64) {
 	sm := a + c
 	df := a - c