[vserver] IPv6 isolation and patch-3.18.5-vs2.3.7.3.diff (and prior)

there is an ipv6 network isolation regression in the 3.18 linux-vserver
patches (as compared to the 3.10 and 3.14 patches), as alex noted on irc [1]
[2] and documented elsewhere [3]. patch-3.18.5-vs2.3.7.3.diff and earlier
are affected.

an available patch [4] fixes the regression as tested using alex's documented
test. it's specifically for 3.18.7-vs2.3.7.3 (as patch-3.18.5-vs2.3.7.3.diff
applies rather cleanly to 3.18.7), but should apply to 3.18.[56]-vs2.3.7.3.

please test and provide feedback.

[1] http://irc.13thfloor.at/LOG/2015-02/LOG_2015-02-12.txt
[2] http://irc.13thfloor.at/LOG/2015-02/LOG_2015-02-13.txt
[3] http://p.animux.de/IqmfxzEMnd9.html
[4] http://vserver.13thfloor.at/Experimental/delta-ipv6udp-fix01.diff

corey

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