In activate routines, don't pre-set the status; set it for all errors.

This fixes some cases where it wasn't being set properly or at all, and
also means that, as it's not being set initially, compilers that do any
dataflow analysis and report uninitialized variables, and static
analyzers, should report cases where we aren't setting variables correctly.

See GH #352.
Always return 0 on a successful activation.
Merge remote-tracking branch 'bpf/master'

bpf.tcpdump.org and GitHub have diverged again.