[enc28j60] rename tp_bits.h -> tp_misc.h to allow adding more utility macros
[enc28j60] tp_bits file rename in macro definition
[enc28j60] add container_of macro to allow fetching context structures from members
[enc28j60] add missing include
[net] add Ethernet interface abstraction
[enc28j60] abstract as etherif_t - not useful yet as ops are directly accessible
[enc28j60] do not expose direct methods - use etherif ops