Change ifconfig_if_up/down() to ifconfig_set_up()

Respond to review comments

This revision shall be closed in favor of D52056 :)

Removed handling IFF_PROMISC when ifi_change=0

I'll reopen this revision to have only IFF_UP related change without touching IFF_PROMISC

I tested it out, it works nicely :)

This revision has been split among:

• https://reviews.freebsd.org/D52130
• https://reviews.freebsd.org/D52131
• https://reviews.freebsd.org/D52128

Since the changes are quite large, I'll split them into smaller revisions :)

Include if_setlladdr error code in err_msg

this revision was opened by mistake :')

• netlink: Modify all flags when ifi_change is 0 in RTM_NEWLINK

In D51871#1185539, @kp wrote:

I'd be inclined to pick up Linux's bug compatibility as well. Presumably there's code out there that makes this incorrect assumption about ifi_change, and we may as well go all out on being compatible. Especially if it's easy to do. That can be done separately if you prefer (or not at all, if either of you have strong views here).

I too think we should have this bug compatibility

This fix has existed out of tree in @obiwac's BATMAN tree
:)

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