Introduce bpf_filter1 function

Function takes additional argument which is a pointer to bpf_aux_data
structure. This newly introduced struct holds auxiliary data provided by caller
to specify additional data needed to implement some BPF extensions while
executing filter in userspace.

bpf_filter1 currently implements support for two BPF extesions, namely
vlan_tci and vlan_pr.
Use BPF extensions in compiled filters

libpcap will generate BPF filter code which uses BPF extensions if target
platform supports them. Currently supported BPF extensions are vlan_tci and
vlan_pr.

Also to properly handle such filters when filtering in userspace libpcap now
employs bpf_filter1.
Merge pull request #391 from msekletar/vlan-bpf

[RFC] Fix vlan filtering on Linux