Add multicast(4) and pim(4) manual pages and hook up to the build.

Submitted by: Pavlin Radoslavov <pavlin@icir.org>
Reviewed by: hsu, bmah
MFC after: 2 weeks

- Merge from HEAD

Merge final round of MLD changes from p4:
ip6_input.c, in6.h:
* Add netinet6-specific mbuf flag M_RTALERT_MLD, shadowing M_PROTO6.
* Always set this flag if HBH Router Alert option is present for

Merge final round of MLD changes from p4:
ip6_input.c, in6.h:
* Add netinet6-specific mbuf flag M_RTALERT_MLD, shadowing M_PROTO6.
* Always set this flag if HBH Router Alert option is present for MLD,
even when not forwarding.

icmp6.c:
* In icmp6_input(), spell m->m_pkthdr.rcvif as ifp to be consistent.
* Use scope ID for verifying input. Do not apply SSM filters here, no inpcb.
* Check for M_RTALERT_MLD when validating MLD traffic, as we can't see
IPv6 hop options outside of ip6_input().

in6_mcast.c:
* Use KAME scope/zone ID in in6_multi.
* Update net.inet6.ip6.mcast.filters implementation to use scope IDs
for comparisons.
* Fix scope ID treatment in multicast socket option processing.
Scope IDs passed in from userland will be ignored as other less
ambiguous APIs exist for specifying the link.
* Tighten userland input checks in IPv6 SSM delta and full-state ops.
* Source filter embedded scope IDs need to be revisited, for now
just clear them and ignore them on input.
* Adapt KAME behaviour of looking up the scope ID in the default zone
for multicast leaves, when the interface is ambiguous.

mld6.c:
* Tighten origin checks on MLD traffic as per RFC3810 Section 6.2:
* ip6_src MAY be the unspecified address for MLDv1 reports.
* ip6_src MAY have link-local address scope for MLDv1 reports,
MLDv1 queries, and MLDv2 queries.
* Perform address field validation *before* accepting queries.
* Use KAME scope/zone ID in query/report processing.
* Break const correctness for mld_v1_input_report(), mld_v1_input_query()
as we temporarily modify the input mbuf chain.
* Clear the scope ID before handoff to userland MLD daemon.
* Fix MLDv1 old querier present timer processing.
With the protocol defaults, hosts should revert to MLDv2 after 260s.
* Add net.inet6.mld.v1enable sysctl, default to on.

ifmcstat.c:
* Use sysctl by default; -K requests kvm(3) if so compiled.

mld.4:
* Connect man page to build.

Tested using PCS.

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Update the projects tree to a newer FreeBSD current.

Merge IGMPv3 and Source-Specific Multicast (SSM) to the FreeBSD
IPv4 stack.

Diffs are minimized against p4.
PCS has been used for some protocol verification, more widespread
testing of recorded sour

Merge IGMPv3 and Source-Specific Multicast (SSM) to the FreeBSD
IPv4 stack.

Diffs are minimized against p4.
PCS has been used for some protocol verification, more widespread
testing of recorded sources in Group-and-Source queries is needed.
sizeof(struct igmpstat) has changed.

__FreeBSD_version is bumped to 800070.

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Add cross-reference to sourcefilter(3).

Point out that PIM is the way to go.

MFC after: 3 days

Update multicast(4) manual page to reflect the new reality of the code.

Polished markup.

Mechanically kill hard sentence breaks and double whitespaces.

Removed trailing whitespace.

Add multicast(4) and pim(4) manual pages and hook up to the build.

Submitted by: Pavlin Radoslavov <pavlin@icir.org>
Reviewed by: hsu, bmah
MFC after: 2 weeks