tor-fw-helper: fix build with golang 1.16

Add GO111MODULE=auto to GO_PKG_BUILD_VARS to allow the package to be
built in non-module mode.

Module-aware mode will be mandatory in the next golang release.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

net/tor-fw-helper/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=tor-fw-helper
 PKG_VERSION:=0.3
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://git.torproject.org/tor-fw-helper.git
@@ -69,6 +69,8 @@ $(call Package/tor-fw-helper/Default/description)
 This package provides the source files for the helper program.
 endef
 
+GO_PKG_BUILD_VARS += GO111MODULE=auto
+
 $(eval $(call GoBinPackage,tor-fw-helper))
 $(eval $(call BuildPackage,tor-fw-helper))