Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

The pr_destroy field does not allow us to run the teardown code in a
specific order. VNET_SYSUNINITs however are doing exactly that.
Thus remove the VIMAGE conditional field from the domain(9) protosw
structure and replace it with VNET_SYSUNINITs.
This also allows us to change some order and to make the teardown functions
file local static.
Also convert divert(4) as it uses the same mechanism ip(4) and ip6(4) use
internally.

Slightly reshuffle the SI_SUB_* fields in kernel.h and add a new ones, e.g.,
for pfil consumers (firewalls), partially for this commit and for others
to come.

Reviewed by: gnn, tuexen (sctp), jhb (kernel.h)
Obtained from: projects/vnet
MFC after: 2 weeks
X-MFC: do not remove pr_destroy
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D6652

Finish r274118: remove useless fields from struct domain.

Sponsored by: Yandex LLC

use .Mt to mark up email addresses consistently (part6)

PR: 191174
Submitted by: Franco Fichtner <franco at lastsummer.de>

Catch up with r186809, correct comments.

Document pffinddomain().

Reviewed by: glebius

Sync with domain and protosw data structures.

Reviewed by: glebius

Catch up with r195837 (2.5 years ago) which renamed net_add_domain() to domain_add().

PR: 165424
Submitted by: Lachlan Kang
MFC after: 1 week

Remove reference to pr_ousrreq from domain(9) since it's now gone from
struct protosw.

Submitted by: bz
MFC after: 3 weeks

pr_pfh has been gone from protosw since r120386 (more than 5 years ago).

MFC after: 4 weeks

Use 'manual page' instead of 'man page' for consistency.

Approved by: re (hrs)

de-__P()

mdoc(7) police: tidy up the markup.

Reviewed by: davidc

Update function definitions and required include files to reflect
the current state of the system.

Approved by: alfred

Add a man page describing the fuctions directly related to network domains.

Reviewed by: alfred