openldap: add a dependency to make do_compile pass

During compiling? we need soelim command provided by groff-native.
So add DEPENDS to fix this issue, else we will get following error:

	/bin/sh: 15: soelim: not found

Signed-off-by: Chong Lu <Chong.Lu@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>