Fix when gatt disconnect too fast, RC pair fail

[Root Cause]
when disconnect too fast and link_state is still DISCONNECTED,
in release_ccb, only lcb released, ACL link will not removed.
When this case happend, disc_comp will have no lcb,
then auto connection will fail cuz last ACL exists.

[Solution]
Set link_state as LST_CONNECTING to avoid this case.

Bug: 264734928
Test: atest net_test_stack_l2cap pass

Change-Id: Ia8e86c3dbaa702c1c115c4e4cb7a21d6955b8aeb