build: fix possible issue with kmod package having multiple AutoLoad's

This commit contains the following changes

 - Use local shell var where appliable
 - The $(sort $$$$$$$$mods) call will have no expected effect
 - Avoid EEXIST when creating symlinks in /etc/modules-boot.d/
 - Avoid duplicate arguments for insert_modules() in postinst-pkg

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

include/kernel.mk

@@ -97,15 +97,16 @@ define ModuleAutoLoad
 	$(SH_FUNC) \
 	export modules=; \
 	probe_module() { \
-		mods="$$$$$$$$1"; \
-		boot="$$$$$$$$2"; \
+		local mods="$$$$$$$$1"; \
+		local boot="$$$$$$$$2"; \
+		local mod; \
 		shift 2; \
-		for mod in $(sort $$$$$$$$mods); do \
+		for mod in $$$$$$$$mods; do \
 			mkdir -p $(2)/etc/modules.d; \
 			echo "$$$$$$$$mod" >> $(2)/etc/modules.d/$(1); \
 		done; \
 		if [ -e $(2)/etc/modules.d/$(1) ]; then \
-			if [ "$$$$$$$$boot" = "1" ]; then \
+			if [ "$$$$$$$$boot" = "1" -a ! -e $(2)/etc/modules-boot.d/$(1) ]; then \
 				mkdir -p $(2)/etc/modules-boot.d; \
 				ln -s ../modules.d/$(1) $(2)/etc/modules-boot.d/; \
 			fi; \
@@ -113,16 +114,17 @@ define ModuleAutoLoad
 		fi; \
 	}; \
 	add_module() { \
-		priority="$$$$$$$$1"; \
-		mods="$$$$$$$$2"; \
-		boot="$$$$$$$$3"; \
+		local priority="$$$$$$$$1"; \
+		local mods="$$$$$$$$2"; \
+		local boot="$$$$$$$$3"; \
+		local mod; \
 		shift 3; \
-		for mod in $(sort $$$$$$$$mods); do \
+		for mod in $$$$$$$$mods; do \
 			mkdir -p $(2)/etc/modules.d; \
 			echo "$$$$$$$$mod" >> $(2)/etc/modules.d/$$$$$$$$priority-$(1); \
 		done; \
 		if [ -e $(2)/etc/modules.d/$$$$$$$$priority-$(1) ]; then \
-			if [ "$$$$$$$$boot" = "1" ]; then \
+			if [ "$$$$$$$$boot" = "1" -a ! -e $(2)/etc/modules-boot.d/$$$$$$$$priority-$(1) ]; then \
 				mkdir -p $(2)/etc/modules-boot.d; \
 				ln -s ../modules.d/$$$$$$$$priority-$(1) $(2)/etc/modules-boot.d/; \
 			fi; \
@@ -131,6 +133,7 @@ define ModuleAutoLoad
 	}; \
 	$(3) \
 	if [ -n "$$$$$$$$modules" ]; then \
+		modules="$$$$$$$$(echo "$$$$$$$$modules" | tr ' ' '\n' | sort | uniq | paste -s -d' ')"; \
 		mkdir -p $(2)/etc/modules.d; \
 		mkdir -p $(2)/CONTROL; \
 		echo "#!/bin/sh" > $(2)/CONTROL/postinst-pkg; \