selftest/bpf: Fix compilation warning in sockmap_parse_prog.c

Remove unused len variable, which causes compilation warnings.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200314001834.3727680-1-andriin@fb.com

tools/testing/selftests/bpf/progs/sockmap_parse_prog.c

@@ -12,7 +12,6 @@ int bpf_prog1(struct __sk_buff *skb)
 	__u32 lport = skb->local_port;
 	__u32 rport = skb->remote_port;
 	__u8 *d = data;
-	__u32 len = (__u32) data_end - (__u32) data;
 	int err;
 
 	if (data + 10 > data_end) {