MFC r288575:

Add IFCAP_LINKSTATE support.

MFC r282809:
Add new socket ioctls SIOC[SG]TUNFIB to set FIB number of encapsulated
packets on tunnel interfaces. Add support of these ioctls to gre(4),
gif(4) and me(4) interfaces. For incoming packets M_SETFIB() should use
if_fib value from ifnet structure, use proper value in gre(4) and me(4).

Differential Revision: https://reviews.freebsd.org/D2462

MFC r276902,282536:
Pass mtag argument into m_tag_locate() to continue the search from
the last found mtag.

MFC r274246:
Overhaul if_gre(4).

Split it into two modules: if_gre(4) for GRE encapsulation and
if_me(4) for minimal encapsulation within IP.

gre(4) changes:
* convert to if_transmit;
* rework locking: protect access to softc with rmlock,
protect from concurrent ioctls with sx lock;
* correct interface accounting for outgoing datagramms (count only payload size);
* implement generic support for using IPv6 as delivery header;
* make implementation conform to the RFC 2784 and partially to RFC 2890;
* add support for GRE checksums - calculate for outgoing datagramms and check
for inconming datagramms;
* add support for sending sequence number in GRE header;
* remove support of cached routes. This fixes problem, when gre(4) doesn't
work at system startup. But this also removes support for having tunnels with
the same addresses for inner and outer header.
* deprecate support for various GREXXX ioctls, that doesn't used in FreeBSD.
Use our standard ioctls for tunnels.

me(4):
* implementation conform to RFC 2004;
* use if_transmit;
* use the same locking model as gre(4);

PR: 164475

MFC r274289 (by bz):
gcc requires variables to be initialised in two places. One of them
is correctly used only under the same conditional though.

For module builds properly check if the kernel supports INET or INET6,
as otherwise various mips kernels without IPv6 support would fail to build.

MFC r274964:
Add ip_gre.h to ObsoleteFiles.inc.

MFC r282809:
Add new socket ioctls SIOC[SG]TUNFIB to set FIB number of encapsulated
packets on tunnel interfaces. Add support of these ioctls to gre(4),
gif(4) and me(4) interfaces. For incoming packets M_SETFIB() should use
if_fib value from ifnet structure, use proper value in gre(4) and me(4).

Differential Revision: https://reviews.freebsd.org/D2462

MFC r276902,282536:
Pass mtag argument into m_tag_locate() to continue the search from
the last found mtag.

MFC r274246:
Overhaul if_gre(4).

Split it into two modules: if_gre(4) for GRE encapsulation and
if_me(4) for minimal encapsulation within IP.

gre(4) changes:
* convert to if_transmit;
* rework locking: protect access to softc with rmlock,
protect from concurrent ioctls with sx lock;
* correct interface accounting for outgoing datagramms (count only payload size);
* implement generic support for using IPv6 as delivery header;
* make implementation conform to the RFC 2784 and partially to RFC 2890;
* add support for GRE checksums - calculate for outgoing datagramms and check
for inconming datagramms;
* add support for sending sequence number in GRE header;
* remove support of cached routes. This fixes problem, when gre(4) doesn't
work at system startup. But this also removes support for having tunnels with
the same addresses for inner and outer header.
* deprecate support for various GREXXX ioctls, that doesn't used in FreeBSD.
Use our standard ioctls for tunnels.

me(4):
* implementation conform to RFC 2004;
* use if_transmit;
* use the same locking model as gre(4);

PR: 164475

MFC r274289 (by bz):
gcc requires variables to be initialised in two places. One of them
is correctly used only under the same conditional though.

For module builds properly check if the kernel supports INET or INET6,
as otherwise various mips kernels without IPv6 support would fail to build.

MFC r274964:
Add ip_gre.h to ObsoleteFiles.inc.