wlan: Avoid connection to an already existing session.

This commit ensures to return a failure on a connection attempt to a
network with which a concurrent interface is already associated.

Change-Id: I94e2fb6091a0e2e8a915fa7041794c0b98c6d785
CRs-Fixed: 550579
diff --git a/CORE/MAC/src/pe/lim/limProcessSmeReqMessages.c b/CORE/MAC/src/pe/lim/limProcessSmeReqMessages.c
index 6cb401a..e0522a1 100644
--- a/CORE/MAC/src/pe/lim/limProcessSmeReqMessages.c
+++ b/CORE/MAC/src/pe/lim/limProcessSmeReqMessages.c
@@ -1650,7 +1650,8 @@
                 // Log the event and send success
                 PELOGW(limLog(pMac, LOGW, FL("Received SME_JOIN_REQ for currently joined BSS"));)
                 /// Send Join success response to host
-                retCode = eSIR_SME_SUCCESS;
+                retCode = eSIR_SME_ALREADY_JOINED_A_BSS;
+                psessionEntry = NULL;
                 goto end;
             }
             else