MFC r270160:

Destroy the "qdiffsample_zone" UMA zone on unload to avoid a use-after-unload
panic easily triggered by running "sysctl -a" after unload.

Reported and tested by:	Grenville Armitage <garmitage@swin.edu.au>
Fix Denial of Service in TCP packet processing.

Security:	FreeBSD-SA-14:19.tcp
Bump __FreeBSD_version after SA-14:19.tcp

Approved by:	re (implicit)
Sponsored by:	The FreeBSD Foundation
MFC r257658 (modified to apply to stable/8):

For C++ programs, don't emit any explicit dependency to libstdc++.a or
libc++.a during the early build stages (bootstrap-tools, build-tools,
cross-tools), since it is not possible to know in advance which C++
library is available on the host system.

Instead, just use the bootstrap compiler's built-in default.  This
should eventually make it possible to build stable/9 on head, or on
stable/10, which ship without libstdc++ by default.

[Note: this should get the stable/8 tinderbox at least a bit further in
buildworld.]
MFH (r271256, r271617): avoid segfault if PAM_RHOST nor PAM_TTY are unset.

PR:             83099
MFC r271492:
Workaround for receiving Voice Calls using the E1750 dongle from
Huawei. It might appear as if the firmware is allocating memory blocks
according to the USB transfer size and if there is initially a lot of
data, like at the answering machine prompt, it simply dies without any
apparent reason. The simple workaround for this is to force a zero
length packet at hardware level after every 512 bytes of data. This
will force the other side to use smaller memory blocks aswell.