SGS2 I9100G keeps disconnecting from WIFI after installing firmware XXLPQ
Well occasionally when you update firmware, your router at home will have problems with the new firmware on your phone (due to out-of-date drivers, old firmware on the router, router is unsupported by new firmware, etc.) So if it works everywhere else pretty well, this might be your issue.

My recommendation: try downloading a different kernel (there are plenty out there for the S2), your best bet looking on the XDA-Forums, maybe start here?

http://forum.xda-developers.com/forumdisplay.php?f=665