libnm: export nm_setting_ip_config_get_dhcp_iaid

Lubomir Rintel requested to merge lr/set-iaid-export into main

The export was left out when the symbol was added; apparently by accident.

Let's also bump the documented version of when is the symbol supposed to be available, because it actually wasn't.

Fixes: 56a1a542 ('all: add ipvX.dhcp-iaid properties')

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