Pull up following revision (requested by riz in ticket #942):
     /sys/net/npf/npf_inet.c		revision 1.23
Fix bugs to prevent panic:
- npf_cache_ip: re-fetch IPv6 header since nbufs might have been reallocated.
- npf_cache_all: clear NBUF_DATAREF_RESET since npf_cache_ip() handles it.
Ticket 942.