Implement missing lowering operators

Currently only a small subset of lowering operators are implemented.  This set should be made complete.  Happily it's not too difficult -- you just compile an expression with libpcap, cross-compile to Lua using the pflua bpf compiler, look at the generated code, then make the pflang compiler do something similar.
The least significant octet in a MAC address can be ommitted. So f:f: is actually f0:f0. Example:

$ tcpdump -d "ether src f:f:f:3:3:3"
(000) ld       [8]
(001) jeq      #0xf030303       jt 2	jf 5
(002) ldh      [6]
(003) jeq      #0xf0f           jt 4	jf 5