sim: bpf: include more local headers & fix broken funcs

sim: bpf: include more local headers & fix broken funcs

Various files were not including the relevant headers, or some funcs
were missing prototypes entirely, leading to mismatch between the
actual definition of the functions.  Add includes to a few places and
fix the broken functions that are uncovered as a result.  Fixing some
compile warnings (e.g. missing prototypes) often find real bugs.