libwimaxll: use @includedir@ in the installed pkg-config file
libwimaxll: use @includedir@ in the installed pkg-config file

Otherwise, if a different dir is set at configure time, the pkg-config
information would be wrong.

Signed-off-by: Inaky Perez-Gonzalez <32fcc484d967529190dea5c4cba96be3030624cc@linux.intel.com>

ago/wimax-tools,susnux/wimax-tools,ago/wimax-tools,susnux/wimax-tools