LinuxKPI: add more linux-specific errno

Add ERFKILL and EBADE found in iwlwifi and brcmfmac wireless drivers.
While here add a comment above the block of error numbers above 500 to
document expectations.

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D29396

(cherry picked from commit 4b0632cfc5c86587668b1d5d2ddc26d445072b03)