SocketHelpers - added dnsIP(n) getter as in WiFi libraries #912

Job	Run time
compile-examples (arduino:mbed:nano33ble)	11m 26s
compile-examples (arduino:mbed:envie_m7)	13m 26s
compile-examples (arduino:mbed:nanorp2040connect)	12m 43s
compile-examples (arduino:mbed:nicla_sense)	11m 51s
compile-examples (arduino:mbed:nicla_vision)	14m 51s
compile-examples (arduino:mbed:opta)	18m 6s
compile-examples (arduino:mbed:giga)	23m 13s
compile-examples (arduino:mbed:nicla_voice)	7m 16s
compile-examples (arduino:mbed:envie_m7:target_core=cm4, - libraries/KernelDebug - libraries/Port...	3m 31s
	1h 56m 23s

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