net: Don't run UDP multicast tests on Alpha GNU/Linux.
net: Don't run UDP multicast tests on Alpha GNU/Linux.

From Uros Bizjak.

R=iant
CC=gofrontend-dev
https://golang.org/cl/5663048

anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,golang/gofrontend