Strip path to the binary from prints.

I see no sense in including the full path in outputs like bpftool --version
Especially as argv[0] may not include it, based on calling via $PATH or not.
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -443 +443,7 @@
-	bin_name = argv[0];
+	/* Strip the path if any. */
+	const char *bin_name_slash = strrchr(argv[0], '/');
+	if (bin_name_slash) {
+		bin_name = bin_name_slash + 1;
+	} else {
+		bin_name = argv[0];
+	}