Create proc_net type for /proc/sys/net entries.

/proc/sys/net could use its own type to help distinguish
among some of the proc access rules. Fix dhcp and netd
because of this.

Change-Id: I6e16cba660f07bc25f437bf43e1eba851a88d538
Signed-off-by: rpcraig <rpcraig@tycho.ncsc.mil>
diff --git a/dhcp.te b/dhcp.te
index 5856a26..e710360 100644
--- a/dhcp.te
+++ b/dhcp.te
@@ -13,7 +13,8 @@
 allow dhcp self:netlink_route_socket { create_socket_perms nlmsg_write };
 allow dhcp shell_exec:file rx_file_perms;
 allow dhcp system_file:file rx_file_perms;
-allow dhcp proc:file write;
+# For /proc/sys/net/ipv4/conf/*/promote_secondaries
+allow dhcp proc_net:file write;
 allow dhcp system_prop:property_service set ;
 allow dhcp dhcp_system_file:file rx_file_perms;
 allow dhcp dhcp_system_file:dir r_dir_perms;