Use bzero instead of explicitly zeroing stuff in do_execve.

While strictly speaking this is not correct since some fields are pointers,
it makes no difference on all supported archs and we already rely on it doing
the right thing in other places.

No functional changes.
Document [EPERM] for UNIX sockets.

MFC after:	2 weeks
Add initial support for the AR9485 CUS198 / CUS230 variants.

These variants have a few differences from the default AR9485 NIC,
namely:

* a non-default antenna switch config;
* slightly different RX gain table setup;
* an external XLNA hooked up to a GPIO pin;
* (and not yet done) RSSI threshold differences when
  doing slow diversity.

To make this possible:

* Add the PCI device list from Linux ath9k, complete with vendor and
  sub-vendor IDs for various things to be enabled;
* .. and until FreeBSD learns about a PCI device list like this,
  write a search function inspired by the USB device enumeration code;
* add HAL_OPS_CONFIG to the HAL attach methods; the HAL can use this
  to initialise its local driver parameters upon attach;
* copy these parameters over in the AR9300 HAL;
* don't default to override the antenna switch - only do it for
  the chips that require it;
* I brought over ar9300_attenuation_apply() from ath9k which is cleaner
  and easier to read for this particular NIC.

This is a work in progress.  I'm worried that there's some post-AR9380
NIC out there which doesn't work without the antenna override set as
I currently haven't implemented bluetooth coexistence for the AR9380
and later HAL.  But I'd rather have this code in the tree and fix it
up before 11.0-RELEASE happens versus having a set of newer NICs
in laptops be effectively RX deaf.

Tested:

* AR9380 (STA)
* AR9485 CUS198 (STA)

Obtained from:	Qualcomm Atheros, Linux ath9k
Remove this stuff - it's no longer needed here.
Make clear in the ipheth(4) hardware notes that this driver is for the
tethering functionality only.  Add a "bugs" section to give a pointer
to usbconfig set_config if the device isn't automatically detected.

MFC after:	3 days
Add a missing file from the last commit.

Noticed by: jhibbits
When plen != ulen, it should only be checked when this is UDP.

Spotted by:	bryanv
Merge remote-tracking branch 'origin/master' into hardened/current/master

Conflicts:
	sys/kern/kern_exec.c (fixed)