libbpf: Switch to void * casting in netlink helpers

Netlink helpers I added in 8bbb77b7c7a2 ("libbpf: Add various netlink
helpers") used char * casts everywhere, and there were a few more that
existed from before.

Convert all of them to void * cast, as it is treated equivalently by
clang/gcc for the purposes of pointer arithmetic and to follow the
convention elsewhere in the kernel/libbpf.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210619041454.417577-2-memxor@gmail.com

src/netlink.c

@@ -524,7 +524,7 @@ static int get_tc_info(struct nlmsghdr *nh, libbpf_dump_nlmsg_t fn,
 	struct nlattr *tb[TCA_MAX + 1];
 
 	libbpf_nla_parse(tb, TCA_MAX,
-			 (struct nlattr *)((char *)tc + NLMSG_ALIGN(sizeof(*tc))),
+			 (struct nlattr *)((void *)tc + NLMSG_ALIGN(sizeof(*tc))),
 			 NLMSG_PAYLOAD(nh, sizeof(*tc)), NULL);
 	if (!tb[TCA_KIND])
 		return NL_CONT;