libwebsockets

LWS_CALLBACK_CLIENT_CLOSED: split out client and server CLOSE callback

Until now LWS_CALLBACK_CLOSED has served the same for
client and server connections.  This introduces a new
LWS_CALLBACK_CLIENT_CLOSE which is sent on established
ws client connections, insread of LWS_CALLBACK_CLOSED.

LWS_CALLBACK_CLOSED continues to be sent when server
ws connections close.