fix: multiple xdp attach to one iface

[mojtaba-esk]

Closes #22

This PR uses the chaining multiple XDP programs method. In reality we load only one xdp_main program which calls the underlying programs in a sequence if a packet is passed by the first program it goes through the next program and it keeps going.

To be able to activate a program (which is tied to a service) is running, we set its map value to something more than zero otherwise the service either is stopped or not started at all.

for example, a zero packet loss rate means it passes all packets and a zero bandwidth means an unlimited bandwidth.
Here is some tests results after making the fix:

Results:
Number of parallel connections per test: 100
Test duration per test: 60 seconds
expected bandwidth: 64 Kbps 	actual bandwidth: 0 bps
expected bandwidth: 128 Kbps 	actual bandwidth: 96 Kbps
expected bandwidth: 256 Kbps 	actual bandwidth: 109 Kbps
expected bandwidth: 512 Kbps 	actual bandwidth: 201 Kbps
expected bandwidth: 1024 Kbps 	actual bandwidth: 0 bps
expected bandwidth: 2 Mbps 	actual bandwidth: 1 Mbps
expected bandwidth: 4 Mbps 	actual bandwidth: 3 Mbps
expected bandwidth: 8 Mbps 	actual bandwidth: 5 Mbps
expected bandwidth: 16 Mbps 	actual bandwidth: 12 Mbps
expected bandwidth: 32 Mbps 	actual bandwidth: 27 Mbps
expected bandwidth: 64 Mbps 	actual bandwidth: 52 Mbps
expected bandwidth: 128 Mbps 	actual bandwidth: 106 Mbps
expected bandwidth: 256 Mbps 	actual bandwidth: 231 Mbps
expected bandwidth: 512 Mbps 	actual bandwidth: 403 Mbps
expected bandwidth: 1024 Mbps 	actual bandwidth: 959 Mbps

Results:
Number of packets per test: 50

Packet loss: 0% 	 Expected: 0%
Packet loss: 4% 	 Expected: 10%
Packet loss: 16% 	 Expected: 20%
Packet loss: 46% 	 Expected: 50%
Packet loss: 60% 	 Expected: 70%
Packet loss: +6 	 Expected: 80%
Packet loss: +29 	 Expected: 100%

As it can be seen, no changes observed in the tests, so the new changes should be ok to go.

[smuu]

Tbh. I don't understand how this works, but if it works, it LGTM 👍