Handle OPTIONS requests from SIP servers.

Change-Id: I849d5ea4c4c56a06d25ccdc6b959274c59c47200
diff --git a/services/java/com/android/server/sip/SipSessionGroup.java b/services/java/com/android/server/sip/SipSessionGroup.java
index b4c2241..03a076c 100644
--- a/services/java/com/android/server/sip/SipSessionGroup.java
+++ b/services/java/com/android/server/sip/SipSessionGroup.java
@@ -349,6 +349,9 @@
                 mProxy.onRinging(newSession, newSession.mPeerProfile,
                         newSession.mPeerSessionDescription);
                 return true;
+            } else if (isRequestEvent(Request.OPTIONS, evt)) {
+                mSipHelper.sendResponse((RequestEvent) evt, Response.OK);
+                return true;
             } else {
                 return false;
             }
@@ -625,6 +628,9 @@
                             (TransactionTerminatedEvent) evt);
                 }
                 return true;
+            } else if (isRequestEvent(Request.OPTIONS, evt)) {
+                mSipHelper.sendResponse((RequestEvent) evt, Response.OK);
+                return true;
             } else if (evt instanceof DialogTerminatedEvent) {
                 processDialogTerminated((DialogTerminatedEvent) evt);
                 return true;