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.

Obtained-from: bz_iwlwifi
Sponsored-by: The FreeBSD Foundation
MFC-after: 2 weeks
Reviewed-by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D29396