rpc: getaddrinfo: also accept IPv4-mapped IPv6 addresses

rpc: getaddrinfo: also accept IPv4-mapped IPv6 addresses

If only IPv6 is configured on the host, getaddrinfo with AI_ADDRCONFIG
in hints would return EAI_ADDRFAMILY for nodenames that resolve to IPv4.

Also pass AI_V4MAPPED to accept IPv4-mapped addresses on IPv6-only
systems.

Signed-off-by: Zhimin Feng <fengzhimin1@huawei.com>
[rewrote the commit message - jtomko]
Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>