kernel-doc: process functions, not DOC:

This flag is necessary for the next patch for docproc to output
only the functions and not DOC: sections when a function list
is requested.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>