Add IPv6 support to O_IP_DST_LOOKUP opcode.

o check the size of O_IP_SRC_LOOKUP opcode, it can not exceed the size of
  ipfw_insn_u32;
o rename ipfw_lookup_table_extended() function into ipfw_lookup_table() and
  remove old ipfw_lookup_table();
o use args->f_id.flow_id6 that is in host byte order to get DSCP value;
o add SCTP ports support to 'lookup src/dst-port' opcode;
o add IPv6 support to 'lookup src/dst-ip' opcode.

PR:		[[ https://bugs.freebsd.org/217292 | 217292 ]]
Sponsored by:	Yandex LLC
Differential Revision:	https://reviews.freebsd.org/D9873