native: mark internal routines

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

Also fix a name and some capitalisation.

native/dlaev2.go

@@ -14,6 +14,8 @@ import "math"
 // and [cs1, sn1] which is the unit right eigenvalue for RT1.
 //  [ cs1 sn1] [a b] [cs1 -sn1] = [rt1   0]
 //  [-sn1 cs1] [b c] [sn1  cs1]   [  0 rt2]
+//
+// Dlaev2 is an internal routine. It is exported for testing purposes.
 func (impl Implementation) Dlaev2(a, b, c float64) (rt1, rt2, cs1, sn1 float64) {
 	sm := a + c
 	df := a - c