MT#55283 use ccflags instead of EXTRA_CFLAGS

EXTRA_CFLAGS is deprecated and stopped working in 6.15(ish)

Ref: https://bugs.debian.org/1106709
Ref: e966ad0edd
Change-Id: Iba835c7dca89106ff2ca7ffba8a7de947c9a4ff8

kernel-module/Makefile

@@ -6,7 +6,7 @@ export M
 
 include $(M)/rtpengine-kmod.mk
 
-EXTRA_CFLAGS+=	-DRTPENGINE_VERSION="\"$(RTPENGINE_VERSION)\""
+ccflags-y    += -DRTPENGINE_VERSION="\"$(RTPENGINE_VERSION)\""
 
 obj-m        += xt_RTPENGINE.o