Any action we take in tap_plug() when using OVS will undo
our rate limiting, which means any hotplug change must
restore the previous rate setting.
Since this means tap_plug() would always be followed by a
tap_rate_limit() call anyway we just include the rate
parameter here and let the caller decide whether the full
tap_plug() is required or the simple tap_rate_limit()
suffices.
read_etc_network_interfaces used the content of
/proc/net/if_inet6 to decide whether an interface's state is
"active", which means an interface is only active when it
has an ipv6 address, thus using net.ipv6.conf.*.disable_ipv6
on an interface will cause it to show as inactive in the web
interface.
We now filter the interfaces found in /proc/dev/net by their
IFF_UP flag read via an SIOCGIFFLAGS ioctl().
We use Net::Ping twice in pve-storage (once for ISCSIPlugin
and once in GlusterfsPlugin, both with the 'tcp' variant.),
but Net::Ping doesn't support IPv6.
