Sometimes an
ifconfig ti0 down /
ifconfig ti0 up helps.
If it doesn't you could ask on the OpenBSD mailing list. Make sure you include the dmesg and the ifconfig output (Inline, not as attachment, because these will be stripped)
Because it is highly probably that you will be asked to try a 4.7 beta snapshot, you could be pro-active and download and install such a 4.7 beta snapshot first.
These snapshots can be found on most of the second level mirrors mentioned in
http://www.openbsd.dk/ftp.html