fix rescue mode on wdr4900

Backport of r48793

brcm2708-gpu-fw: move pkg build dir to kernel build dir to fix rebuild bugs after cleaning the kernel tree

Backport of r48732

The bootloader of AirOS 5.6.x doesn't remove the flash protection for us,
so we have to do this ourselves.

This should fix problems with flashing from AirOS 5.6.x.

Backport of r47591 and r48427

Should be redundant after 0bd0df6f

Signed-off-by: Felix Kaechele <felix@kaechele.ca>

We're too close to the release of Gluon 2016.1 to do a full update of our
OpenWrt tree, therefore just make a backport of this.

Also remove the BROKEN check as the UniFi Outdoor Plus support seems to
work fine now.

Fixes #272

Fixes #177

Fixes #589

OpenSSL moves old versions of the library from http://www.openssl.org/source/
to http://www.openssl.org/source/old/1.0.2/ breaking the old links. That
behavior breaks the OpenWRT-build every time OpenSSL releases a new version.

This patch adds http://www.openssl.org/source/old/1.0.2/ to the PKG_SOURCE_URL
of OpenSSL to avoid breaking the build whenever OpenSSL releases a new
version.

This patch is already included in the current OpenWrt CC branch.
Cherry-pick for now as we're very close to the Gluon 2015.2 release.

The trunk version of mac80211 doesn't need these dependencies anymore as
they are compiled into the kernel.

While this didn't cause any issues for Gluon as we always build the kernel
with all modules, this fix makes the patch work on a plain OpenWrt CC as
well.

Fixes #550

Fixes #540

Update kernel to 3.18.23

ath9k expects to get revision id 2 for the QCA9531 ver. 2 rev. 0. This
fixes the very low TX power on some devices like the TP-LINK
TL-WR841ND v10.

As ath79_soc_rev is only used to get the revision number to ath9k on the
QCA9533, just set it to the expected value on the ver. 2.

Some more cleanup.