Added support for ingress traffic shaping

[shreyasar2202]

This PR addresses #287. The way ingress traffic shaping is done is by using virtual interfaces - IFBs.

• The virtual interfaces created are linked to the test interfaces such that there is a one-to-one mapping between a virtual interface and a test interface.
• Then, incoming traffic to each test interface is forced to first pass through the corresponding virtual interface. Linux's tc commands are then used to performing egress traffic control on the virtual interface.
• Since the outbound traffic from the virtual interface passes through the test interface, this is effectively ingress traffic control. After a certain time interval, the traffic is restored to normal

[janosdebugs]

Tentative approval, please add filtering for the parameters to the "tc" commands so they match ^[a-z0-9]+$ to avoid possible shell injections.

[sandrobonazzola]

LGTM

[shreyasar2202]

Tentative approval, please add filtering for the parameters to the "tc" commands so they match ^[a-z0-9]+$ to avoid possible shell injections.

I've used ^[a-z0-9\-\@\_]+$as some interfaces seem to have @, _ and - as well