iwmbtfw(8): Improve Intel 7260/7265 adaptors handling
- Allow firmware downloading for hw_variant #8;
- Enter manufacturer mode for setting of event mask;
- Handle multi-event response on HCI commands for 7260; This allows to remove kludge with skipping of 0xfc2f opcode.
- Disable patch and exit manufacturer mode on downloading failure;
- Use default firmware if correct firmware file is not found;
Reviewed by: Philippe Michaud-Boudreault <pitwuu_AT_gmail_DOT_com>
MFC after: 1 week
Tested by: arrowd
Differential revision: https://reviews.freebsd.org/D30543
(cherry picked from commit da93a73f834612b659b37b513c8296e1178d249b)