Don't require searches by IPv6 address to start with [

Searches by IPv6 address need to include [], and partial searches need to start with [. Example: "[2001:858:2:2:aabb:0:563b:1526]". That's not as intuitive as it could be. We should consider making the [] part optional for IPv6 searches. Not sure if that's a good idea, but I can't come up with major arguments against it.

This enhancement request originates from legacy/trac#10128 (moved) and has low priority.