l2cap: Improve ECOC creation handling

With this patch we make sure that L2CA_ConnectCreditBasedReq will fail
if there is ongoing connection request.
Also, handling of the peer ConnectCreditBasedResponse is improved in the
way, that user can call connect already in the
pL2CA_CreditBasedConnectCfm_Cb or pL2CA_Error_Cb

Found during PTS testing

Bug: 242032465
Test: PTS Testing
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: I80347b1281947a4830020fe9a1f70f21a57400fc