add prototype functions for missing wl_data_offer interface
add prototype functions for missing wl_data_offer interface

As we require wayland 1.10 now, there were missing functions for
wl_data_offer interface. This patch just adds placeholders for those
missing functions until we can implement them

Signed-off-by: Chris Michael <2c9adca9bdb4861297f022d161a6a7c2d4597bd5@osg.samsung.com>

rvandegrift/e,rvandegrift/e,tasn/enlightenment,tasn/enlightenment,rvandegrift/e,tasn/enlightenment