iwlwifi: dbg: add op_mode callback for collecting debug data.

The first use is collecting debug data when transport stops the device.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210210142629.d282d0a9ee7b.I9a0ad29f80daba8956a6aa077ba865e19b2150be@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>