tests: more options for decoding pcaps

Introduce "none", "all" and "failed" options for --decode-pcaps
parameter. Keep "failed" as default to be consistent with current
behaviour. Add missing documentation to test/Makefile and passthrough to
Makefile.

Rationale: running tshark binary takes about 100-150ms and if there are
thousands of pcap files, it takes minutes to decode them. This might not
be desirable if rerunning the tests repeatedly during development.

Type: improvement
Change-Id: Ie033521d51d18b9d499b9bc40fe6eff21c94622d
Signed-off-by: Klement Sekera <klement.sekera@gmail.com>
diff --git a/test/config.py b/test/config.py
index 32cc4ca..e939f18 100644
--- a/test/config.py
+++ b/test/config.py
@@ -409,10 +409,11 @@
     "/var/run/user/${uid}/vpp.",
 )
 
-default_decode_pcaps = False
+default_decode_pcaps = "failed"
 parser.add_argument(
     "--decode-pcaps",
-    action="store_true",
+    action="store",
+    choices=["none", "failed", "all"],
     default=default_decode_pcaps,
     help=f"if set, decode all pcap files from a test run (default: {default_decode_pcaps})",
 )