Specify a hostname for the SSL hostname check

[matthiasklein]

Due to the "prefer ip4 addresses" (see issue https://github.com/eclipse/paho.mqtt.c/issues/1396), the idea arose to perform name resolution outside of the PAHO library in the application.

For example, the "happy eyeballs" algorithm could be implemented in the application. Then only an IP address and port would be passed to the PAHO library.

The corresponding hostname would then have to be passed separately to enable SSL hostname verification.

[freebendy]

I am hitting the same issue. My application has own DNS resolve logic so I resolve the hostname outside paho and pass IP address to it. And I got error MQTTAsync_rcv: PAHO trace: SSL error: <00132D9C:error:0A000126:SSL routines:ssl3_read_n:unexpected eof while reading:../openssl-3.0.12/ssl/record/rec_layer_s3.c:303:. I think this because IP address is set via SSL_set_tlsext_host_name and it failed the name verification.