ksmbd: add ipv6_addr_v4mapped check to know if connection from client is ipv4

ksmbd create socket with IPv6 to listen both IPv4 and IPv6 connection
from client. Server should send IP addresses of NICs through network
interface info response. If Client connection is IPv4, Server should
fill IPv4 address in response buffer. But ss_family is always PF_INET6
on IPv6 socket. So This patch add ipv6_addr_v4mapped check to know
client connection is IPv4.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>