Show SFP+/QSFP memory map dump on higher verbose levels.

Sponsored by:	Yandex LLC
MFC after:	1 week
Clean up (refactor) discovery a little; no functional changes.

MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
vt(4): Add PIO_VFONT_DEFAULT ioctl to restore the default builtin font

To restore the default font using vidcontrol(1), use the "-f" flag
without an argument:
    vidcontrol -f < /dev/ttyv0

PR:		193910
Differential Revision:	https://reviews.freebsd.org/D971
Submitted by:	Marcin Cieslak <saper@saper.info>
Reviewed by:	ray@, emaste@
Approved by:	ray@
MFC after:	1 week
Fix a bug where some DTS layouts could cause the premature ending of the
search (i.e. without returning any result) and you would end up with a
random MAC address.

Change the search algorithm to a recursive one to ensure that all the nodes
on DTS will be verified.

The previous algorithm could not keep up if the DTS has too many sub-nodes.

While here, fix the punctuation on comments.
Move if_get_counter initialization from if_attach into if_alloc.
Also, initialize all counters before ifnet will become available in the system.
This fixes possible access to uninitialized ifned fields.

PR:		194550
Change the code to use the openpty(3) API which uses the pts(4) driver
instead of the pty(4) driver.

PR:		184597
Submitted by:	tobias.rehbein
MFC after:	2 weeks
Avoid taking the lock in selfdfree when not needed.