adding :
net.tcp.buffersize.default=4096,87380,256960,4096,16384,256960
net.tcp.buffersize.wifi=4096,87380,256960,4096,16384,256960
net.tcp.buffersize.umts=4096,87380,256960,4096,16384,256960
net.tcp.buffersize.gprs=4096,87380,256960,4096,16384,256960
net.tcp.buffersize.edge=4096,87380,256960,4096,16384,256960
(without the spaces) to build.prop causes bootloop here
I have this and it works great for me:
# Net Speed Tweaks
net.tcp.buffersize.default=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.wifi=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.umts=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.gprs=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.edge=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.hspa=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.lte=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.hspda=524288,1048576,2097152,524288,1048576,2097152
net.tcp.buffersize.evdo_b=524288,1048576,2097152,524288,1048576,2097152