tools: bpftool: print only one error message on byte parsing failure

Make error messages more consistent. Specifically, when bpftool fails at
parsing map key bytes, make it print a single error message to stderr
and return from the function, instead of (always) printing a second
error message afterwards.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/bpf/bpftool/map.c

@@ -252,7 +252,7 @@ static char **parse_bytes(char **argv, const char *name, unsigned char *val,
 		val[i] = strtoul(argv[i], &endptr, 0);
 		if (*endptr) {
 			err("error parsing byte: %s\n", argv[i]);
-			break;
+			return NULL;
 		}
 		i++;
 	}