MFC r339462: make upgrade from previous FreeBSD versions less painful
and make previously working configuration like this work again:

gif_interfaces="gif0"
gifconfig_gif0="1.1.1.1 2.2.2.2"
ifconfig_gif0="inet 192.168.1.1 192.168.1.2 netmask 255.255.255.252"

PR: 204700

Fix breakage in r325799 that removed a bit of code by my mistake.

Approved by: avg (mentor)

MFC r325559: ifconfig_<interface>_descr

Add suitable knob ifconfig_<interface>_descr for static interface description.
Document availability of interface descriptions within rc.conf(5).

Approved by: avg (mentor)

MFC r278933:
Fix a typo in ipv6_down().

Submitted by: Ashutosh Kumar AK0037447 at TechMahindra.com

MFC r266267, r267636:

Fix an issue in range specification handling when a "-foo" is specified in
ifconfig_IF_aliasN.

MFC r265225:

Move configuration of IPv6 NDP flags to a point before handling ifconfig_IF.
This fixes a race that a non-IPv4 interface can get an EUI64 LLA even if it
has IFDISABLED nd6 flag at boot time.

MFC r271424:

- Add $netif_ipexpand_max to specify the upper limit for the number of
addresses generated by an address range specification. The default value
is 2048. This can be increased by setting $netif_ipexpand_max in rc.conf.

PR: 186841

MFC r267812 (hrs): Fix ifname normalization. ifconfig_IF_alias{es,N} did not
work if ifname has any of [.-/+].

While here, also perform the following to reduce diff size between major
branches for etc/network.subr:

MFC r266475 (rea): Fix warning messages after r252015

$alias used to hold alias number, but now it carries full variable name,
so messages were tuned to account for that.

Other fixes:
- eliminate unneeded double spaces;
- tell user where inet/inet6 keywords are expected to be.

Reviewed by: hrs
Spotted by: jhay
PR: conf/191961

MFC r264243:

Loosen the processing of *_IF_aliasN vars to be less strict. Previously,
the first alias had to be _alias0 and processing stopped at the first non-
defined variable (preventing gaps). Allowing gaps gives the administrator
the ability to group aliases in an adhoc manner and also lifts the
requirement to renumber aliases simply to comment-out an existing one.
Aliases are processed in numerical ascending order.

NB: Also Patches mdconfig{,2} rc(8) boot scripts to loosen the numbering
scheme for mdconfig_mdN settings to be less strict in the same manner.

Discussed on: -rc

MFC r278933:
Fix a typo in ipv6_down().

Submitted by: Ashutosh Kumar AK0037447 at TechMahindra.com

MFC r266267, r267636:

Fix an issue in range specification handling when a "-foo" is specified in
ifconfig_IF_aliasN.

MFC r265225:

Move configuration of IPv6 NDP flags to a point before handling ifconfig_IF.
This fixes a race that a non-IPv4 interface can get an EUI64 LLA even if it
has IFDISABLED nd6 flag at boot time.

MFC r271424:

- Add $netif_ipexpand_max to specify the upper limit for the number of
addresses generated by an address range specification. The default value
is 2048. This can be increased by setting $netif_ipexpand_max in rc.conf.

PR: 186841

MFC r267812 (hrs): Fix ifname normalization. ifconfig_IF_alias{es,N} did not
work if ifname has any of [.-/+].

While here, also perform the following to reduce diff size between major
branches for etc/network.subr:

MFC r266475 (rea): Fix warning messages after r252015

$alias used to hold alias number, but now it carries full variable name,
so messages were tuned to account for that.

Other fixes:
- eliminate unneeded double spaces;
- tell user where inet/inet6 keywords are expected to be.

Reviewed by: hrs
Spotted by: jhay
PR: conf/191961

MFC r264243:

Loosen the processing of *_IF_aliasN vars to be less strict. Previously,
the first alias had to be _alias0 and processing stopped at the first non-
defined variable (preventing gaps). Allowing gaps gives the administrator
the ability to group aliases in an adhoc manner and also lifts the
requirement to renumber aliases simply to comment-out an existing one.
Aliases are processed in numerical ascending order.

NB: Also Patches mdconfig{,2} rc(8) boot scripts to loosen the numbering
scheme for mdconfig_mdN settings to be less strict in the same manner.

Discussed on: -rc