Bluetooth: reorganize functions from hci_sock_sendmsg()

Since userfaultfd mechanism allows sleeping with kernel lock held,
avoiding page fault with kernel lock held where possible will make
the module more robust. This patch just brings memcpy_from_msg() calls
to out of sock lock.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>