lint: sh: add checking for initscripts

Detect initscripts by their shebang line. SC2034 is ignored additionally
for these scripts, to avoid needing to override it for setting START,
USE_PROCD, ... in every single script.

scripts/lint-sh.sh

@@ -6,6 +6,10 @@ is_scriptfile() {
 	echo "$1" | grep -q '\.sh$' || head -n1 "$1" | grep -qE '^#!(.*\<bash|/bin/sh)$'
 }
 
+is_initscript() {
+	head -n1 "$1" | grep -qxF '#!/bin/sh /etc/rc.common'
+}
+
 find contrib -type f | while read -r file; do
 	is_scriptfile "$file" || continue
 
@@ -14,10 +18,13 @@ find contrib -type f | while read -r file; do
 done
 
 find package -type f | while read -r file; do
-	is_scriptfile "$file" || continue
-
+	if is_scriptfile "$file"; then
 		echo "Checking $file"
 		shellcheck -f gcc -x -s sh -e SC2039,SC3043,SC3037,SC3057 "$file"
+	elif is_initscript "$file"; then
+		echo "Checking $file (initscript)"
+		shellcheck -f gcc -x -s sh -e SC2034,SC2039,SC3043,SC3037,SC3057 "$file"
+	fi
 done
 
 find scripts -type f | while read -r file; do