Duplicate packets for Loopback interfaces

[fako1024]

It's a known issue that on loopback devices all packets are duplicated (for both ring buffer and non ring buffer sources) because the kernel observes all packets as both incoming and outgoing on the interface. Technically this makes sense, but it is accepted standard (e.g. in libpcap and other packet capture solutions) to drop the outgoing duplicate packets.
In order to be in line with that standard slimcap should handle this automatically (and at the same time use the opportunity to supply packet type filtering capabilities, that way it's a win-win).

DoD

• Extend Link by packet filter mask
• Automatically filter outgoing packet duplicates for loopback interfaces

[fako1024]

Closed by merging #67