update external/Makefile to build with latest NDK r8e

* olsrd's make/Makefile.android still has the old variables, but this works
  around that by sending in correct values via the make command line

* this now will default to a 64-bit NDK on a 64-bit system. To override
  that, set NDK_PROCESSOR=x86 on the make command line
update busybox config for new version that Andrew included

Whenever the busybox submodule gets updated, the external/busybox_config
file needs to be updated.  I updated it by manually running the build,
then answering the questions about the new features, then running:

  cp external/busybox/.config external/busybox_config

Then committing the changes to external/busybox_config