Move the definitions of "bootp_flag_values[]" and "bootp_op_values[]"

Move the definitions of "bootp_flag_values[]" and "bootp_op_values[]"
out of "bootp.h" into "print-bootp.c", so we don't get unused copies of
them in files other than "print-bootp.c" that include "bootp.h", and so
we don't get warnings from GCC 3.3 about those unused copies.