lei: make pkt_op easier-to-use and understand

lei: make pkt_op easier-to-use and understand

Since switching to SOCK_SEQUENTIAL, we no longer have to use
fixed-width records to guarantee atomic reads.  Thus we can
maintain more human-readable/searchable PktOp opcodes.

Furthermore, we can infer the subroutine name in many cases
to avoid repeating ourselves by specifying a command-name
twice (e.g. $ops->{CMD} => [ \&CMD, $obj ]; can now simply be
written as: $ops->{CMD} => [ $obj ]  if CMD is a method of
$obj.