Why same file in multiple locations in kernel code?

I have downloaded kernel 5.0 kernel code, and looking for file netlink.h. I see file with same name is present in multiple sub-directories. Which file do I need to #include if I write a netlink based program ?

3 include/linux/netlink.h
6 include/net/netlink.h
9 include/uapi/linux/can/netlink.h
f include/uapi/linux/netlink.h
l net/batman-adv/netlink.h
q net/tipc/netlink.h

Can somebody pls help to give me some insight regarding org of kernel src tree.