You've to correct sdram_init to use 128MB as described here: http://oleg.wl500g.info/sdram.html
But there are several problems: 1) stock firmware hangs trying to detect 128MB due to a bug; 2) I've not much experience with upgrading WL700gE RAM, but have number of WL500gP upgraded to 128MB. Some of them does not boot without capacitor (about 4pF) added to pin 51 of U4 to correct bad PCB tracing. Perhaps wl700ge traced better.