Fixed hyperlink for IPs shown in IP ban list

Simple correction for a typo in the generation of the hyperlink.

Without:
```index.php?action=viewip&player=2.103.174.209&server=0``` (results in redirect to index.php)

With:
```index.php?action=viewip&ip=2.103.174.209&server=0``` (correctly shows ban history etc for IP)

Example:
http://www.frostcast.net/banmanagement/index.php?action=searchip&server=0&player=%
Any of the IPs are effectively dead links.