init: add "+passcred" for socket to set SO_PASSCRED

In the init scripts for socket, the type can have a suffix of
"+passcred" to request that the socket be bound to report SO_PASSCRED
credentials as part of socket transactions.

Test: gTest logd-unit-tests --gtest_filter=logd.statistics right after boot
      (fails without logd.rc change)
Bug: 37985222
Change-Id: Ie5b50e99fb92fa9bec9a32463a0e6df26a968bfd
diff --git a/init/service.cpp b/init/service.cpp
index 4d9edc4..296c04c 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -525,7 +525,9 @@
 
 // name type perm [ uid gid context ]
 bool Service::ParseSocket(const std::vector<std::string>& args, std::string* err) {
-    if (args[2] != "dgram" && args[2] != "stream" && args[2] != "seqpacket") {
+    if (!android::base::StartsWith(args[2], "dgram") &&
+        !android::base::StartsWith(args[2], "stream") &&
+        !android::base::StartsWith(args[2], "seqpacket")) {
         *err = "socket type must be 'dgram', 'stream' or 'seqpacket'";
         return false;
     }