drivers/network/wlan: Import idualwifi7260 from FreeBSD 11.2.

The lowest model number supported by this driver is "3160", but that's just
Intel's insanity: the 7260 was released the quarter before it. So following
our naming convention strictly, "7260" is the correct name for this driver.

The firmware situation for this one is also a little different. Unlike past
instances where Intel has released mostly nonsubstantial firmware updates,
allowing us to just copy a recent-ish version from the iwlwifi archives,
the firmware is more closely tied to the driver in this series. As a result,
some of this firmware is not even used by Linux yet (they're a few versions
behind it seems), so the firmware packages included here come from FreeBSD.

One major hardware feature - RX of multiple frames at a time - is disabled
in this commit, as it depends on mbuf reference-counting, according to the
FreeBSD developers I asked, which we do not implement yet. I'll hopefully
get to looking at that in the next few weeks.

And with that, I finally have WiFi on my primary laptop, my original reason
for setting out on this quest last year. This commit was pushed through it,
even :)

build/jam/images/definitions/minimum

@@ -204,6 +204,7 @@ SYSTEM_ADD_ONS_DRIVERS_NET = [ FFilterByBuildFeatures
 		aironetwifi atheroswifi
 		broadcom43xx
 		iprowifi2100 iprowifi2200 iprowifi3945 iprowifi4965
+		idualwifi7260
 		marvell88w8363 marvell88w8335
 		ralinkwifi
 		wavelanwifi