Golangcilint in build pipeline and fix lint errors

- Fix bad permissions bits for files
- VPNSP is 'private internet access' instead of 'pia' (retro compatible)
- Check errors of deferred unsetEnv functions in params package
-  Other lint errors fixing and code simplifications

internal/openvpn/tun.go

@@ -30,7 +30,7 @@ func (c *configurator) CreateTUN() error {
 	if err := c.mkNod(string(constants.TunnelDevice), unix.S_IFCHR, int(dev)); err != nil {
 		return err
 	}
-	if err := c.fileManager.SetUserPermissions(string(constants.TunnelDevice), 666); err != nil {
+	if err := c.fileManager.SetUserPermissions(string(constants.TunnelDevice), 0666); err != nil {
 		return err
 	}
 	return nil