validate IP address in pmpro_get_ip

[andrewlimaza]

• ENHANCEMENT: Validate the user's IP address using filter_var and check if it's IPV4 or IPV6 within the pmpro_get_ip function.

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[andrewlimaza]

This is mainly for the Local Pricing Add On, and ensuring that the data returned from this method is an actual IP address. It helps us validate the returned data without extra checks when calling the method.