pf: Update packet filter to the version that comes with OpenBSD 4.1

pf: Update packet filter to the version that comes with OpenBSD 4.1

    The original OpenBSD 4.1 defaults to "keep state flags S/SA" for
    all pass rules. In contrast to that we default to "no state". As
    in earlier verions of pf in DragonFly the default keep-state
    policy can still be set with the keep-policy option (e.g. "set
    keep-policy keep state (pickups)").

    DragonFly additions to pf have been kept: fairq support,
    pickups.

	Detailed Info on changes/additions:
	* ALTQ: Fix altq to work with pf_mtag
		Patch by Matthew Dillon
	* libkern: Revert commit e104539
		strchr was added to libkern.h together with strrch
	* net/if.h: add interface groups
		Imported from FreeBSD.
	* netinet6/in6.h: add macros
		IN6_IS_ADDR_MC_INTFACELOCAL
		IN6_IS_SCOPE_EMBED
		PV6_ADDR_SCOPE_INTFACELOCAL
	* sys/libkern.h: Add strchr and strrchr as inline functions
		Brought in from FreeBSD
	* sys/net/if_var.h: Import interface groups
		Import interface groups and event handlers from FreeBSD
	* sys/net/if_var.h: add if_pf_kif, if_groups to struct ifnet
		obtained from: Open/FreeBSD
	* net/if_types.h: add IFT_ENC to non-IATA-assignments
		obtained from Open/FreeBSD
	* net/bpf.c: add bpf_mtap_hdr from OpenBSD
		Con up a minimal dummy header to pacify bpf.  Allocate
		(only) a struct m_hdr on the stack.