Addition of 'LvlDiscard Lvl = -1' at beginning of const block in commit

e699254 caused the iota assigned values of LvlCrit through LvlTrace to change from 0 to 5 to 1 to 6. (ethereum#815)

This restores the original enumerated const values by moving LvlDiscard after all the iota assigned constants.
Usage of auto-increment enumerations does not work the same way in golang as it does in C/C++ and its behaviour is detailed in the link below.
https://go.dev/ref/spec#Iota

log/logger.go

@@ -18,13 +18,13 @@ const skipLevel = 2
 type Lvl int
 
 const (
-	LvlDiscard Lvl = -1
-	LvlCrit    Lvl = iota
+	LvlCrit Lvl = iota
 	LvlError
 	LvlWarn
 	LvlInfo
 	LvlDebug
 	LvlTrace
+	LvlDiscard Lvl = -1
 )
 
 // AlignedString returns a 5-character string containing the name of a Lvl.