Use kmemdup rather than duplicating its implementation.

./net/bluetooth/hci_conn.c:1880:7-14: WARNING opportunity for kmemdup.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=5597Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>