Fix DNS module not working with --disable-ipv6

[vanosg]

Found by: raclure
Patch by: Geo, thommey
Fixes: #93 #207

One-line summary:
setsockname should return AF_UNSPEC when allowres is 0, which the DNS module uses to do non-blocking DNS lookups.

Test cases demonstrating functionality (if applicable):

Fixed not-resolving hostnames with --disable-ipv6:

[19:59:42] Trying server [sinisalo.freenode.net]:6667
[19:59:42] DNS Resolver: Lookup successful: sinisalo.freenode.net
[19:59:42] DNS resolved sinisalo.freenode.net to 91.217.189.42

Additionally, instead of treating an IPv6 as a hostname, it now skips resolution and returns an error

[19:38:04] Trying server [2001:778:627f::1:0:49]:6667
[19:38:04] ERROR: Attempted to use IPv6 address, but IPv6 is not enabled on this eggdrop
[19:38:04] Warning: Can't create new socket: Address family not supported by protocol!
[19:38:04] ERROR: Attempted to use IPv6 address, but IPv6 is not enabled on this eggdrop
[19:38:04] Failed connect to 2001:778:627f::1:0:49 (Bad file descriptor)

[vanosg]

The first approach was, in @thommey 's (summarized) words was "all wrong". Also, we discovered inet_pton() is not reliably present on a non-IPv6 OS, so we shouldn't use it when --disable-ipv6 is used. Thus, we have this approach when --disable-ipv6 is used:

Jumping servers......
[20:55:43] Trying server [2a00:1a28:1100:11::42]:6667
[20:55:43] ERROR: This looks like an IPv6 address, but this Eggdrop was not compiled with IPv6 support.
[20:55:43] Failed connect to 2a00:1a28:1100:11::42 (Operation now in progress)

and the other use cases:

[20:56:44] Trying server [irc.freenode.net]:6667
[20:56:44] Connected to irc.freenode.net
[20:56:44] -NOTICE- *** Looking up your hostname...

[21:14:27] Trying server [193.219.128.49]:6667
[21:14:27] Connected to 193.219.128.49
[21:14:27] -NOTICE- *** Looking up your hostname...