allow ot_daemon to read/write sockets shared by system_server

system_server creates an ICMPv6 socket and send it to ot_daemon via ParcelFileDescriptor. ot_daemon will use that socket to send/receive ICMPv6 messages.

Here's how the socket is created in System Server:
int sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

Bug: 294486086

Security consultation bug: 296809188

Test: Verified on a cuttlefish

Change-Id: I9d479c9da01187a0e476591f447f7199ecb3a409
diff --git a/private/ot_daemon.te b/private/ot_daemon.te
index cdf5486..1021fd9 100644
--- a/private/ot_daemon.te
+++ b/private/ot_daemon.te
@@ -20,6 +20,9 @@
 # Allow OT daemon to read/write the Thread tunnel interface
 allow ot_daemon tun_device:chr_file {read write};
 
+# Allow OT daemon to read/write on the socket created by System Server
+allow ot_daemon system_server:rawip_socket rw_socket_perms_no_ioctl;
+
 hal_client_domain(ot_daemon, hal_threadnetwork)
 
 # Only ot_daemon can publish the binder service