Try changing the 0x06 into 0x10 if you use the mkgmap lines style sheet. This should renderer the line into a cyclepath instead of an unclassified road. In this way you can check whether this works.

edit:
I just looked up the lines in the standard mkgmap lines style sheet. There is no 0x10 line in it mentioned. So the line will not rendered or will be visible as a line. You can try 0x16 (footpath) or 0x0a (track).