Add missing frees in argument parsing

[PlagueCZ]

There were some edge cases where freeing of command-line argument memory was not properly done.

No real-world implication as this is just before the process exits anyway.

• DHCPv6 DNS options were never freed
• if dp_service.conf contains some options that allocate memory, then before actual command-line parsing the process fails, that memory would never be freed
• if one mellanox option (in the config fileú does not properly allocate, the other mellanox options would not get freed

[byteocean]

thanks for fixing.

[guvenc]

@PlagueCZ would you please rebase ?