Really disable IPv6 RA processing in dhcpcd.

IPv6 RA processing in dhcpcd causes crashes, so we disabled it in
dhcpcd.conf. Unfortunately devices sometimes don't have the
config file, because one is not required for dhcpcd to work. So
disable IPv6 RA processing in the code too.

(cherry picked from commit 69eb1982f233676775ccb8718fc62e78c137e33d)

Bug: 15268738
Bug: 15779617
Change-Id: I67bce5fb27f6b7c4e3189285baeda639256c9079
(cherry picked from commit e0eb380913f6f24b011322d00aff261999bc465b)

Author: Pierre Imai

if-options.c

@@ -796,7 +796,13 @@ read_config(const char *file,
 	ifo = xzalloc(sizeof(*ifo));
 	ifo->options |= DHCPCD_GATEWAY | DHCPCD_DAEMONISE | DHCPCD_LINK;
 	ifo->options |= DHCPCD_ARP | DHCPCD_IPV4LL;
+#ifndef ANDROID
+	/* On Android, don't enable IPv6 RS processing. This is because we
+	 * already process RAs in the kernel and netd and because we've seen
+	 * dhcpcd crashes when parsing certain RA options.
+	 * See http://b/15268738 and http://b/15779617 . */
 	ifo->options |= DHCPCD_IPV6RS | DHCPCD_IPV6RA_REQRDNSS;
+#endif
 	ifo->timeout = DEFAULT_TIMEOUT;
 	ifo->reboot = DEFAULT_REBOOT;
 	ifo->metric = -1;