ipv6: udp: convert 'connected' to bool type in udpv6_sendmsg()

This should make it consistent with ip6_sk_dst_lookup_flow()
that is accepting the new 'connected' parameter of type bool.

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>