conf: don't pass interface type into virNetDevBandwidthParse

conf: don't pass interface type into virNetDevBandwidthParse

The virNetDevBandwidthParse method uses the interface type to decide
whether to allow use of the "floor" parameter. Using the interface
type is not convenient as callers may not have that available, but
still wish to allow use of "floor". Switch to an explicit boolean
to control its usage.

Reviewed-by: Laine Stump <laine@laine.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>