If we have an entry in users file like this:
<TAB>Framed-IP-Address<TAB> = 188.8.131.52
it will fail saying "Invalid attribute name", while it looks completely OK (as tabs are invisible and quite valid as whitespace everywhere else).
It did work long time ago (v2.2 at least) but it does not now (3.0.1+), and the relevant code is here: https://github.com/FreeRADIUS/freeradius-server/blob/278306422eda760c0b06385b0508461b3034652c/src/lib/valuepair.c#L1981
Be less picky about attribute names. Closes #796