.b4-config: Add checkpatch.pl default commands

Blend b4 default checkpatch.pl flags with the ones defined in
include/mk/env_post.mk in .b4-config so that a contributor may use `b4 prep
--check` and `b4 am --check` in his workflow.

Signed-off-by: Ricardo B. Marliere <rbm@suse.com>
Reviewed-by: Andrea Cervesato <andrea.cervesato@suse.com>

Author: rbmarliere

.b4-config

@@ -4,3 +4,6 @@
     send-series-to = Linux Test Project <ltp@lists.linux.it>
     pw-url = https://patchwork.ozlabs.org/
     pw-project = ltp
+    prep-perpatch-check-cmd = ./scripts/checkpatch.pl -q --terse --no-summary --mailback --showfile --no-tree --ignore CONST_STRUCT,VOLATILE,SPLIT_STRING,FILE_PATH_CHANGES
+    am-perpatch-check-cmd = ./scripts/checkpatch.pl -q --terse --no-summary --mailback --no-tree --ignore CONST_STRUCT,VOLATILE,SPLIT_STRING,FILE_PATH_CHANGES
+