kernel: handle optional backport for selinux_inode

* For supporting kernel 4.19 with 5.10 bpf backports.

Signed-off-by: rsuntk <rsuntk@yukiprjkt.my.id>

kernel/Makefile

@@ -103,10 +103,13 @@ endif
 ifeq ($(shell grep "ssize_t kernel_write" $(srctree)/fs/read_write.c | grep -q "const void" ; echo $$?),0)
 ccflags-y += -DKSU_OPTIONAL_KERNEL_WRITE
 endif
+ifeq ($(shell grep -q "inode_security_struct\s\+\*selinux_inode" $(srctree)/security/selinux/include/objsec.h; echo $$?),0)
+$(info -- KernelSU: kernel has selinux_inode.)
+ccflags-y += -DKSU_OPTIONAL_SELINUX_INODE
+endif
 ifeq ($(shell grep -q "int\s\+path_umount" $(srctree)/fs/namespace.c; echo $$?),0)
 ccflags-y += -DKSU_HAS_PATH_UMOUNT
 endif
-
 # Checks Samsung UH drivers
 ifeq ($(shell grep -q "CONFIG_KDP_CRED" $(srctree)/kernel/cred.c; echo $$?),0)
 ccflags-y += -DSAMSUNG_UH_DRIVER_EXIST