namequery: correctly merge kdc ip address list

namequery: correctly merge kdc ip address list

When finding DCs, there are three sources of addresses:
1. "Last good server"
2. Configured password server
3. SRV DNS queries

Since those different sources may return the same addresses, the
IP list is checked for duplicates, e.g. in order to save on
the LDAP ping that usually follows. Both IP address and port are
compared.

This change fixes the address duplicate removal for the case of KDC
search, where the "last good server" or configured password server
also appears in the DNS SRV query response.

An (undocumented?) assumption is that the "password server" parameter
is applicable to KDCs as well, but if a port is specified (e.g.
dc1.example.com:390), then this is the ldap port.

Signed-off-by: Uri Simchoni <urisimchoni@gmail.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>