udev: introduce TxQueueLength= setting

Enable udev to set the transmit queue length of a device via a new directive to
be used in link files. The kernel stores this parameter as an unsigned 32 bit
integer. As typical values currently range in the order of 10 to a few 10,000
packets reduce the domain of valid values for this directive to 0..4294967294
and take the excluded 4294967295 == UINT32_MAX to indicate that the directive
is unset.