LE: Do not invoke callback if retrying read/write operation

When a descriptor read/write operation fails with insufficient
authentication/encryption, it will automatically be tried again with
elevated security requirements. The first (failed) attempt should not be
reported to the application requesting the read/write, since it will get
the 2nd callback once the retry succeeds/fails.

Change-Id: Ia27b91afa63b6f9ffdc597d59c24d29f3d8a1008