Update release notes with FAB-18250

Signed-off-by: Brett Logan <brett.t.logan@ibm.com>

release_notes/v1.4.9.md

@@ -69,6 +69,15 @@ chaincodes always require a channel context. This fix ensures that
 a channel context is available for calls to user chaincodes, and
 returns an error if the client did not pass a channel name.
 
+**FAB-18250: Introduce error checking for evicting invalid PKCS11 sessions**
+
+FAB-17722 introduced a call to the pkcs11 GetSessionInfo function for retrieving the current state of
+the PKCS11 session. The result of this function was used to determine whether a session was still
+valid to perform HSM operations or if it should be evicted from the session pool. Performance tests
+showed that the call to GetSessionInfo was computationally prohibitively expensive. FAB-18242 reverted 
+this change and FAB-18250 introduced a new method for determining if the PKCS11 session is invalid.
+Now when an HSM operation fails, we check the resultant error against the known session error codes and 
+evict the session from the pool if the error was the result of an invalid session. 
 
 Dependencies
 ------------