Allow pfi_kif_get() callers to pre-allocate buffer for new kif. If kif

Allow pfi_kif_get() callers to pre-allocate buffer for new kif. If kif
object exists already, then caller must free the pre-allocated buffer.
If caller does not pre-allocate buffer, the pfi_kif_get() will get
memory from pool using M_NOWAIT flag.

Commit is  also polishing pfi_initialize() a bit so it uses M_WAITOK
allocation for pfi_all.

there is no change in current behaviour.

feedback by bluhm@

OK bluhm@