doc: Fox Doxygen to filter out __attribute__ from source before parsing
doc: Fox Doxygen to filter out __attribute__ from source before parsing

Turns out Doxygen doesn't like those we use the pre-processor to filter
them out (only for Doxygen)

Signed-off-by: Sylvain Munaut <349f318521b45672c77207abf1a5ed60eb011db1@246tNt.com>

marcelmaatkamp/docker-gnuradio-osmocom-gmr,marcelmaatkamp/gnuradio-osmocom-gmr,marcelmaatkamp/docker-gnuradio-osmocom-gmr,marcelmaatkamp/gnuradio-osmocom-gmr,marcelmaatkamp/gnuradio-osmocom-gmr,marcelmaatkamp/docker-gnuradio-osmocom-gmr