Fix a typo in the length check for session_enc_key

proxy/proxy.go

@@ -138,7 +138,7 @@ func (c *Configuration) check() error {
 		return errors.New("session_auth_key must be a random string of 32 or 64 bytes")
 	}
 	switch len(c.SessionEncKey) {
-	case 16, 24, 43:
+	case 16, 24, 32:
 	case 0:
 		return errors.New("session_enc_key is empty")
 	default: