write changes some parts of the config, if this is a reference to the
config used for checking parsing it may lead to unexpected failures
due to those side effects..
For me it was "cidr" and "cidr6" getting deleted, and thus upcomming
tests for a compat change failing without any apparent reason.. :/
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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().
