The function is used to parse a tuple delimited by commas into
virNetDevBandwidth structure. So far only three out of fore
fields are supported: average, peak and burst. The single missing
field is floor. Well, the parsing works, but I think we can do
better. Especially when we will need to parse floor too in very
close future.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>