Now flushes the RX buffer twice.

This is based on the errata sheet and both the TinyOS and Contiki
implementations.

Fixes issue #15.
removing whitespace at end of lines
Merge branch 'flushrx' of github.com:bradjc/linux-cc2520-driver into flushrx
revamped printk system

Changed ioctl to allow for variable amount of debug printing at
cc2520.ko runtime. This way applications can completely turn off debug
output, or enable full debug output without having to recompile the
module.

Defaults to INFO level printing, as before.
removing old printk #defines