docs/conf.py: silence autosectionlabel duplicate-label warnings

sphinxarg.ext generates generic sub-headings ("Named arguments",
"Positional arguments", "Sub-commands", "General options", ...) for
every argparse command and tool.  These repeat across many files and
trigger large numbers of autosectionlabel duplicate-label warnings.

Two-pronged fix:

* `autosectionlabel_maxdepth = 3` eliminates the depth-4+ warnings
  (sub-headings inside each individual command block).
* `suppress_warnings` per file silences the residual depth-3 collisions
  ("serial reader", "decode_hex", "sub-commands", ...) that still
  appear across tool documentation files.

Cross-references into these generic argparse-generated sections are not
a supported use-case, so suppressing the warnings is appropriate.

Change-Id: I9cdf2a4f6cbd435b16b90ab668205600ffd7c3b0

docs/conf.py

@@ -64,3 +64,20 @@ html_theme = 'alabaster'
 html_static_path = ['_static']
 
 autoclass_content = 'both'
+
+# Workaround for duplicate label warnings:
+# https://github.com/sphinx-doc/sphinx-argparse/issues/14
+#
+# sphinxarg.ext generates generic sub-headings ("Named arguments",
+# "Positional arguments", "Sub-commands", "General options", ...) for every
+# argparse command/tool.  These repeat across many files and trigger tons
+# of autosectionlabel duplicate-label warnings - suppress them.
+autosectionlabel_maxdepth = 3
+suppress_warnings = [
+    'autosectionlabel.saip-tool',
+    'autosectionlabel.shell',
+    'autosectionlabel.smpp2sim',
+    'autosectionlabel.smpp-ota-tool',
+    'autosectionlabel.suci-keytool',
+    'autosectionlabel.trace',
+]