ng_ubt: Do not clear stall before receiving of HCI command response.

Unconditional execution of "clear feature" request at SETUP stage was
workaround for probe failures on ng_ubt.ko re-kldloading which is
unnecessary now.

Reviewed by: hselasky
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D29775

(cherry picked from commit 52489f2a55e625ea35bccc3749ca3adad6ce0c54)