Related work items: #1240, #1241, #1258, #1260, #1270, #1271, #1272, #1279, #1286, #1288, #1289, #1292, #1293, #1294, #1295, #1297, #1298, #1299, #1301, #1305, #1307, #1308, #1309, #1310, #1313, #1314, #1315, #1318, #1320, #1321, #1322, #1324, #1326, #1328, #1332, #1333, #1334, #1335, #1337

…1301)

Most of the code in /internal/guest has build tags as it's all Linux specific
so apply one for vsock.go as well as vsock.Dial is unimplemented on Windows.

This also fixes a linter issue we've been seeing on the push trigger for
golangci-lint. It complains that the error check we're performing can
never be true (err == nil) because on linting this file with GOOS=windows
it will check the Windows implementation for vsock.Dial which is hard coded
to return an unimplemented error always.

Signed-off-by: Daniel Canter <dcanter@microsoft.com>