Do not do additional dev_ref() on the newly created interface in the
if_clone create method [1]. This reference is not needed and never
removed, causing struct cdevpriv leakage. Remove the setting of
SI_CHEAPCLONE flag as well, since it is unused.
For dev_clone handlers, create cdevs with the call make_dev_credf(MAKEDEV_REF)
instead of calling make_dev() and then dev_ref(), to avoid a race.
Call drain_dev_clone_events() at the module unload time after dev_clone
handler is deinstalled.
Submitted by: Mikolaj Golub <to.my.trociny gmail com> [1]
MFC after: 1 week
22e62e7e6e