luci-base: sys.uc: reliably skip TIME_WAIT connections in conntrack list

The TIME_WAIT indicator might not appear at the beginning of the tuple
string in some cases, so match it anywhere.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
[add commit message]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>