A follow-on from #46171 (add unit test for isc_inet_pton), the unit tests for these functions should be extended to check they detect invalid input and return the correct error codes.  Conditions that should be checked are:

inet_pton
* Invalid address family
* Invalid address for family (e.g. AF_INET with a V6 address)
* Invalid address in correct format (e.g. 1.2.3.456)
* NULL passed as address argument
* Empty address argument
* Invalid address argument

inet_ntop
* Buffer too small to accept result