Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r268867, r268878:

Use more consistent type for optlen in getsourcefilter()

Proposed by: bde

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use the LLINDEX macro to access the link-level I/F index. This makes
it possible to work with a different type for the sdl_index field --
it only requires a recompile.

Obtained from: Juniper Networks, Inc.

Fix an obvious bug in getsourcefilter()'s use of struct __msfilterreq;
the kernel will return in msfr_nsrcs the number of source filters
in-mode for a given multicast group.
However, the filters themselves were never copied out, as the libc
function clobbers this field with zero, causing the kernel to assume
the provided vector of struct sockaddr_storage has zero length.
This bug would only affect users of SSM multicast, which is shimmed
in 7.x.
Picked up during mtest(8) refactoring.

MFC after: 1 day

Update copyright.

Fix missing prototype warnings. (Compile errors with -Werror on)
When using namespace.h/un-namespace.h, you use _ versions of syscalls.
Change getsockopt() to _getsockopt() and same for setsockopt().

Approved by: re

Fix a typo which crept in from an earlier version of this file.

Add missing userland support files from previous commit for the new
multicast source filter API functions.