Fix fallback_time option (#562)

Fallback time option was updating request_time instead of fallback_time.

Resolves #561

Author: ColinMcInnes

src/if-options.c

@@ -2546,7 +2546,7 @@ parse_option(struct dhcpcd_ctx *ctx, const char *ifname, struct if_options *ifo,
 #ifdef INET
 	case O_FALLBACK_TIME:
 		ARG_REQUIRED;
-		ifo->request_time =
+		ifo->fallback_time =
 		    (uint32_t)strtou(arg, NULL, 0, 0, UINT32_MAX, &e);
 		if (e) {
 			logerrx("invalid fallback time: %s", arg);