* [SSDP] add `schema(Print &) const`
Supercedes #2806
Make SSDP::schema(WiFiClient&) use a by-ref (reduce stack use)
Add a SSDP::schema(Print&)
From @Palatis' original PR:
useful when using AsyncWebServer.
* Use ip.toString, only export Print& schema interface
Because WiFiClient inherits a Print interface, replace the
::schema(WiFiClient&) with ::schema(Print&) which is source compatible
with existing code and allows the functionality requested in the initial
PR.
Use ip.toString() in the templates instead of breaking up the octets of
the address.
* Fix compile errors and backwards compatibility