drivers/nrf802154: do not filter broadcast PAN ID

[jia200x]

Contribution description

This changes were (almost) cherry-picked from #18156. It addresses three things:

• It fixes CCA result (before was just throwing garbage)
• It fixes a variable initialization
• It prevents the broadcast PAN ID being filtered.

These commits are required in order to run #18156.

Testing procedure

• Try running the cca command in tests/ieee802154_hal. It should report a mixture of "BUSY" and "CLEAR".
• Set the PAN address of any node to the PAN broadcast (0xffff). The node should still be able to receive frames.

Issues/PRs references

#18156