Snap length as option (TODO)

[jonschipp]

Add snap length like tcpdump has to truncate a packet by n bytes.
This is for user convenience as it won't have to be done in BPF.
e.g. Write 96 bytes of each packet to file.pcap: $ netsniff-ng --in eth0 --out file.pcap --snap-length 96

[expressoCoder]

Related to this issue, if snap-length or different parameter was used to set maximum size of packet in RX_RING buffer. I'm capturing multiple 10 Gbps interfaces and memory gets used up fast