tools: add style checking scripts

Add shell script and modified checkpatch.pl for use with patch files
targeting FRR.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>

tools/checkpatch.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+# Check a patch for style errors.
+# Usage:
+#	./checkpatch.sh <patch>
+checkpatch="./checkpatch.pl --no-tree -f"
+
+git status | grep "working directory clean"
+if [ $? -ne 0 ]; then
+	echo "[!] git working directory must be clean."
+	exit 1
+fi
+
+mkdir -p f1 f2
+bash -c "cd .. && git apply $1 2> /dev/null"
+mod=$(git ls-files -m .. | grep ".*\.[ch]")
+cp $mod f1/
+git reset --hard
+cp $mod f2/
+for file in f1/*; do
+  $checkpatch $file > "$file"_cp 2> /dev/null
+done
+for file in f2/*; do
+  $checkpatch $file > "$file"_cp 2> /dev/null
+done
+for file in f1/*_cp; do
+  diff $file f2/$(basename $file) | grep -A3 "ERROR\|WARNING"
+done
+rm -rf f1 f2