Add __attribute__((format)) to the declarations of the ndo_printf,

Add __attribute__((format)) to the declarations of the ndo_printf,
ndo_error, and ndo_warning function pointers in a netdissect_options
structure.

Fix some errors adding that caught.

Have the RRCP dissector extract fields itself, with the EXTRACT_ macros
and a u_char pointer, rather than printing numbers from a structure
which doesn't put structure members on natural boundaries
(__attribute__((packed)) doesn't help, as not all compilers support it)
- note also that not all processors support dereferencing unaligned
pointers, e.g. SPARC - and assuming some fields are in the "right" byte
order.  Also have it check whether data is available in the packet
before referring to it.