Fix: httpc set_options override

[MarkoMin]

The bug was due to invalid validation of options that was acting like the user always passed ipfamily and unix_socket options, so each time when calling set_option(s) those options would get overridden by default values (if option values weren't present in the new options list).

Validation of ipfamily and unix_socket combination was not just buggy, but also insufficient because the httpc state could end up with invalid combination of those options which I proved in the httpc_SUITE:invalid_ipfamily_unix_socket/1 testcase (which fails on the current code). I also believe that there was a typo in httpc:validate_ipfamily_unix_socket/1 where ipfamily option got deleted twice, but unix_socket was not, so we could end up having two unix_socket entries after validation....

With the new behavior that checks current and new options httpc can't end up having invalid ipfamily-unix_socket combo. I also believe that new error is more informative to the user on what's going on and why validation failed.

I also removed deprecated ipv6 handling in httpc_manager because ipv6 gets translated to ipfamily option in httpc:validate_options/3 so there is no way that ipv6 entry can ever be passed to httpc_manager. httpc_manager:set_options is called only from httpc:set_options which validates (and translates) ipv6 option so this should be safe.

Closes #8829

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CT Test Results

  2 files   22 suites   10m 39s ⏱️
350 tests 345 ✅  5 💤 0 ❌
620 runs  569 ✅ 51 💤 0 ❌

Results for commit 7f4340a.

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[MarkoMin]

maybe seems like a perfect fit here