NDK: Add makefiles

Running ndk-build from the app directory will build nflog.  Tested with
NDK r9.
nflog: exit if stdin gets closed

This prevents stale nflog processes from hanging around when AFWall
terminates.
nflog: Flush stdout after each message

By default, printf() and similar functions will perform buffered output,
delaying AFWall's receipt of the log entry.  To avoid this, just invoke
fflush() from the callback.
nflog: Update binary to match the latest source changes
NflogService: Don't rely on caller to set nflogPath

Under some circumstances the service may start up on its own, before
applySavedIptablesRules() is able to set up the path.  The result looks
like:

    I/AFWall  ( 2983): nflog shell started
    D/AFWall  ( 3065): Starting null

Of course, if we try to run "null" instead of the nflog utility, then no
logs will be generated.
Merge pull request #198 from cernekee/nflog-v2

NFLOG fixes