net: udp: remove redundant initialization in udp_send_skb

The initialization for 'err' with 0 is redundant and can be removed,
as it is updated by ip_send_skb and not used before that.

Signed-off-by: Menglong Dong <dong.menglong@zte.com.cn>
Link: https://lore.kernel.org/r/1604644960-48378-4-git-send-email-dong.menglong@zte.com.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>