[vserver] Kernel build failures with IPv6 as a module

Hi,

I'm getting a build failure after applying any of the most recent
vserver patches, for instance
http://vserver.13thfloor.at/Experimental/patch-4.9.135-vs2.3.9.8.diff.
I've tracked the cause down to the fact that I have IPv6 support
configured as a module and the vserver code uses statements like
#if CONFIG_IPV6
rather than the kernel macro
#if IS_ENABLED(CONFIG_IPV6)

I'm wondering if this a bug, or if it perhaps not make sense to
configure IPv6 as a module in the vserver context?

Apologies if I'm asking a stupid question, I'm new to vserver!

-- 
Chris Richardson, System Architect
cr@fourc.eu
FourC AS, Vestre Rosten 81, Trekanten, NO-7075 Tiller, Norway
www.fourc.eu
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