[libfko/test suite] add the FUZZING_INTERFACES macro

Add a new fko_set_encoded_data() function gated by #define
FUZZING_INTERFACES to allow encryption and authentication to be bypassed
for fuzzing purposes (and only fuzzing purposes).  The fko-wrapper code
has been extended to process data in the
test/fko-wrapper/fuzz_spa_payloads file, which is created by the new
python fuzzer.  Typical workflow is:

$ cd test/fko-wrapper
$ ../spa_fuzzer.py > fuzz_spa_payloads
$ make fuzzing

(as root):

./test-fwknop.pl  --enable-profile-coverage --enable-fuzzing-interfaces --enable-all --include wrapper

[+] Starting the fwknop test suite...

    args: --enable-profile-coverage --enable-fuzzing-interfaces --enable-all --include wrapper

    Saved results from previous run to: output.last/

    Valgrind mode enabled, will import previous coverage from:
        output.last/valgrind-coverage/

[+] Total test buckets to execute: 2

[Rijndael] [fko-wrapper] multiple libfko calls (with valgrind)......pass (1)
[Rijndael] [fko-wrapper] multiple libfko calls......................pass (2)
[profile coverage] gcov profile coverage............................pass (3)
[valgrind output] [flagged functions] ..............................pass (4)

    Run time: 5.85 minutes

[+] 0/0/0 OpenSSL tests passed/failed/executed
[+] 0/0/0 OpenSSL HMAC tests passed/failed/executed
[+] 4/0/4 test buckets passed/failed/executed

test/fko-wrapper/Makefile

@@ -2,5 +2,8 @@
 all : fko_wrapper.c
 	gcc -Wall -g -I../../lib fko_wrapper.c -o fko_wrapper -L../../lib/.libs -lfko
 
+fuzzing: fko_wrapper.c
+	gcc -Wall -g -DFUZZING_INTERFACES -I../../lib fko_wrapper.c -o fko_wrapper -L../../lib/.libs -lfko
+
 clean:
 	rm -f fko_wrapper