clib.h: Added malloc(3) comment.
packet.free(): free associated buffers too.
port.lua: Removed temp debug code.
buffer.lua: Allocate 'struct buffer' with malloc() instead of ffi.new().

This fixes a bug where buffers would be garbage collected by Lua while
still in use. Now they live forever.
intel10g.lua: Tighten data structures, remove temp debug code.

dev.txpackets and dev.rxbuffers are now C arrays rather than Lua tables.