Previous to this change a check was done for base64 characters in incoming
SPA data only up to MIN_SPA_DATA_SIZE. This check may be reinstantiated for
SPA packets that are delivered over HTTP (and the packet data is embedded
within a URL that may also contain non-base64 chars), but in the meantime the
fwknopd daemon should not accept SPA packets over arbitrary ports with any
non-base64 chars.
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