When we call `tc` function for creating the HTB QDisc with NO kwargs,
the kernel will return error 22 (invalid argument)::

	 ip.tc("add", "htb", eth0, 0x10000)
	 pyroute2.netlink.exceptions.NetlinkError: (22, 'Invalid argument')

As you can see by calling the `tc` function without any additional
arguments (we only defined `command`, `kind`, `index` and `handle`
arguments) the module will raise `NetlinkError`; reason: according to
'net/sched/sch_htb.c' of linux kernel source code, to create a HTB
QDisc we also need to define `direct_pkts`, `rate2quantum` and
`defcls` which is not defined by default (the function `get_parameters`
is responsible for providing these default arguments which WON'T be
called unless we have at least ONE argument in kwargs.

Bug-Url: https://github.com/svinota/pyroute2/pull/308