nimble/l2cap: Fix locking when receiving LE CoC credit update
nimble/l2cap: Fix locking when receiving LE CoC credit update

Lets remove lock once we have conn and chan.
Functions ble_l2cap_coc_continue_tx() and ble_l2cap_sig_disconnect()
do own locking when needed,

X-Original-Commit: f902592a8e83030111a5555be12530a681ca6b97

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble