lb: backend traffic should not be classified/filtered

[vdmit11]

Currently, the classification/filtering functions are called for all sockets owned by the Tempesta FW.

However, they should be called only for client sockets. There is not much sense in filtering the internal backend traffic. Usually we can trust the internal network and would not like to inspect its traffic.

[krizhanovsky]

Actually, we do need to process backend traffic and WAF is one of the cases. Rather classification logic should just skip packets which aren't interesting for its analyzing.