virnetdevbandwidth.c: Put a limit to "quantum"

virnetdevbandwidth.c: Put a limit to "quantum"

The "quantum" attribute of HTB is documented as:

  Number of bytes to serve from this class before the scheduler
  moves to the next class.

Since v1.3.2-rc1~225 we compute what we think is the appropriate
value and pass it on the TC command line. But kernel and
subsequently TC use uint32_t to store this value. If we compute
value outside of this type then TC fails and prints usage which
we then interpret as an error message. Needlessly long error
message. While there's not much we can do about the latter, we
can put a cap on the value and stop tickling this behavior of TC.

Fixes: 065054daa71f645fc83aff0271f194d326208616
Resolves: https://issues.redhat.com/browse/RHEL-34112
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>