add support for netem qdisc and fw filter

Limited support yet, not all options are supported
netem only supports loss, delay
[netem] add corruption,reorder and correlation features
Merge pull request #17 from chantra/pyroute2_netem

merge netem code from @chantra
netem: pep8 fix
Merge pull request #1 from svinota/netem

master rebase and pep8 fix for netem branch
[netem] sanity checks the arguments

Also add scripts/sample_packet_04.data that contains the message
sent over the link when running:
tc qdisc add dev eth1 handle 8002: parent 1:2 netem limit 1000 delay 50.0ms  51.0ms 50% loss 2% 50% reorder 25% 0.5% corrupt 25% 5% gap 1
[fw] only defined options are set, make get_fw_parameter generic
Merge pull request #18 from chantra/pyroute2_netem

netem implementation