golang has enabled RFC 6555 Fast Fallback (aka HappyEyeballs)
by default in 1.12.
It means that if a host resolves to both IPv6 and IPv4,
it will try to connect to any of those addresses and use the
working connection.
However, the implementation uses go routines to start both connections in parallel,
and this has limitations when running inside a namespace, so we try to the connections
serially, trying IPv4 first for keeping the same behaviour.
xref https://github.com/golang/go/issues/44922
Signed-off-by: Antonio Ojea <aojea@redhat.com>
305b425830