etc/dists/scripts/debian-add_ip.sh: improve removing of IPv6 address

Commit 9612a0121 changed the logic of adding an IPv6 address to Debian CT.
This patch adds some enhancements to it:
 - adding a comment telling what we do
 - make the grep regex stricter: we want the line to start with a tab
   and a space after add/del
 - also remove "down ifconfig venet0 del" line which was not removed

http://bugzilla.openvz.org/1669

Cc: Michael Fincham <michael@unleash.co.nz>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
1 file changed