package/pkg-golang: use package go env for download step

Currently package secific go env is used only during package build step.

Go vendering is done during the download step and it's sometimes required
to specify package secific go env also for this step.

For example, when importing custom go modules who are hosted on a private
host, it’s required to set GOPRIVATE to avoid public sum checking.

Of all the environment variables driving the behaviour of the go command
[0], there is none that obviously have an impact on the behaviour of
go-mod, unless they are explicitly listed as such [1], so it seems
pretty safe to include the generic environment variables for the
download step.

[0] https://pkg.go.dev/cmd/go#hdr-Environment_variables
[1] https://go.dev/ref/mod#environment-variables

Signed-off-by: Patrick Gerber <pge@ik.me>
[yann.morin.1998@free.fr: add [0] and [1] and corresponding blurb]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/pkg-golang.mk

@@ -87,7 +87,8 @@ $(2)_POST_PATCH_HOOKS += $(2)_GEN_GOMOD
 $(2)_DOWNLOAD_POST_PROCESS = go
 $(2)_DL_ENV += \
 	$$(HOST_GO_COMMON_ENV) \
-	GOPROXY=direct
+	GOPROXY=direct \
+	$$($(2)_GO_ENV)
 
 # Due to vendoring, it is pretty likely that not all licenses are
 # listed in <pkg>_LICENSE.