Support running Gatekeeper and Grantor on KVM

While running Gatekeeper on KVM, a couple of issues have been identified.

The following log entry is likely the biggest issue here since it means that Gatekeeper is not properly parsing packets.
`GATEKEEPER: l2: gk: invalid Ethernet field or frame not Ethernet II:38`
The current L2 implementation in Gatekeeper doesn't support alternatives to Ethernet II.

IPv6 multicast addresses in the format `0x33-33-mm-mm-mm-mm` are not being properly handled. Log entry example:
```
GATEKEEPER: acl: a packet failed to match any ACL rules, the whole packet is dumped below:
dump mbuf at 0x10f09c040, iova=5769c0d0, buf_len=2176
pkt_len=90, ol_flags=0, nb_segs=1, in_port=1
segment at 0x10f09c040, data=0x10f09c150, data_len=90
Dump data at [0x10f09c150], len=90
00000000: 33 33 00 00 00 16 FE 54 00 4B 73 5F 86 DD 60 00 | 33.....T.Ks_..`.
00000010: 00 00 00 24 00 01 00 00 00 00 00 00 00 00 00 00 | ...$............
00000020: 00 00 00 00 00 00 FF 02 00 00 00 00 00 00 00 00 | ................
00000030: 00 00 00 00 00 16 3A 00 05 02 00 00 01 00 8F 00 | ......:.........
00000040: FB DF 00 00 00 01 04 00 00 00 FF 02 00 00 00 00 | ................
00000050: 00 00 00 00 00 01 FF 4B 73 5F | .......Ks_
```
Information about these multicast addresses can be found in the article [Mapping IPv6 Multicast Addresses to Ethernet Addresses](https://flylib.com/books/en/2.223.1.44/1/). One has to investigate if Gatekeeper has to do something with these packets or just silently dropping them.

See [this Gatekeeper log](https://github.com/AltraMayor/gatekeeper/files/6266772/gatekeeper_2021_04_05_19_36.log) for examples of the issues described above.

Supporting KVM will enable Gatekeeper to be deployed on more cloud providers and be an easier alternative to test Gatekeeper.