[syslog] Add support for IPv6 syslog server

Note that IANA has not yet assigned a DHCPv6 option code for the
syslog server.  When a code is assigned, the definition of
DHCPV6_LOG_SERVERS should be updated.  Until then, an IPv6 address of
a syslog server can be configured manually using e.g.

  set syslog6 3ffe:302:11:2::8309

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/tcp/syslogs.c

@@ -49,7 +49,6 @@ struct console_driver syslogs_console __console_driver;
 
 /** The encrypted syslog server */
 static struct sockaddr_tcpip logserver = {
-	.st_family = AF_INET,
 	.st_port = htons ( SYSLOG_PORT ),
 };