Previously, the isccc_ccmsg_invalidate() was called from conn_free() and
this could lead to netmgr calling control_recvmessage() after we
detached the reading controlconnection_t reference, but it wouldn't be
the last reference because controlconnection_t is also attached/detached
when sending response or running command asynchronously.
Instead, move the isccc_ccmsg_invalidate() call to control_recvmessage()
error handling path to make sure that control_recvmessage() won't be
ever called again from the netmgr.
2d2c249958