Remove duplicate bandwidth limit validity checks

Bandwidth limit validity was defined once on loading and once on
setting. Setting cannot be practically used to also check on load
because initialization that uses the limits is required to set them
later.
Fix crash on load of very large bandwidth limits

A very large bandwidth limit was causing an invalid argument to
TokenBucket, and the IllegalArgumentException it throws was not handled
during loading. This showed up when someone entered a long string of 9s
for an incoming bandwidth limit.

It still doesn't proceed to work, as there isn't a default suitable to
all cases, but a controlled exit is better than an uncaught and
unexplained exception.