.b4-config: check patches with ./utils/check-package

NOTE: This requires `b4` version 0.14.2 or later as earlier versions had
a bug that broke custom prep-perpatch-check-cmd[1].

If a check-cmd is declared, `b4` will warn developers to run the patch
checker before sending a patch series[2][3]. Developers can then run `b4 prep
--check` to automatically run ./utils/check-package on only files
modified in the patch series.

[1] https://github.com/mricon/b4/commit/0741bc9a5b45578e4d3804588dd3f63fe4848059
[2] https://b4.docs.kernel.org/en/latest/contributor/send.html#passing-pre-flight-checks-v0-14
[3] https://b4.docs.kernel.org/en/latest/config.html#contributor-oriented-settings

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

.b4-config

@@ -3,5 +3,6 @@
 [b4]
     send-series-to = buildroot@buildroot.org
     send-auto-cc-cmd = "./utils/get-developers -e -"
+    prep-perpatch-check-cmd = "./utils/check-package -q -p -"
 
 # vim: set filetype=gitconfig: