nghttpx: Add client-no-http2-cipher-black-list option

This commit adds client-no-http2-cipher-black-list option to disable
enforcement of HTTP/2 cipher black list on backend HTTP/2 connection.
Previously, existing no-http2-cipher-black-list option disables it for
both frontend and backend connections.  Now no-http2-cipher-black-list
option only disables it for frontend connection.

gennghttpxfun.py

@@ -155,6 +155,7 @@ OPTIONS = [
     "frontend-keep-alive-timeout",
     "psk-secrets",
     "client-psk-secrets",
+    "client-no-http2-cipher-black-list",
 ]
 
 LOGVARS = [