Tinydtls had its own .gitignore file that masked away two
include files that are needed in compilation. Removed
the files from ignore file and added those two files.
Change-Id: Ibcfcf4e18ca8f56eef97d41464c4233148e9db9e
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>