L2cap Signalling manager: Fix OnCommandReject

Checking command_just_sent_.command_code_ !=
command_reject_view.GetCode() doesn't make sense because
command_just_sent_.command_code_ is never CommandReject, but XyzRequest,
where command_reject_view.GetCode() is always CommandReject. We
shouldn't check it here.

Bug: 145707677
Test: cert/run --host
Change-Id: I424a8f715ef49372762c6df870d9c63de3b8c597