Change sec_state before resend pending command

Description:
When phone trigger rfcomm create connection during pairing, the create
connection command will be saved to pending command array and wait for
resend.
When authentication completed, btm_sec_change_pairing_state is called to
change the pair state to idle and then resend the command in pending
command array if any. After that, stack set the sec_state to idle if
needed. (If sec_state is not idle, it means we are authenticating or
encrypting)

The issue is the resend command will not work as expected in function
btm_sec_execute_procedure because sec_state is not set to idle yet.

Solution:
Reorder the flow in btm_sec_auth_complete to make sure sec_state set to
idle if needed before invoking btm_sec_change_pairing_state(which resend
the command in the pending command array). And also set sec_flags to
BTM_SEC_AUTHENTICATED to avoid redundant authentication.

Bug: 131108715
Test: run sl4a to create rfcomm connection during pairing
(cmd)bta_bond
(cmd)rfcomm_connect <uuid>

Change-Id: I2521225610506db294d2ad8769f256705a4afaaa