Bluetooth: l2cap: fix 1 byte infoleak to userspace

Structure l2cap_options has one padding byte between max_tx and
txwin_size fields.  This byte in "opts" is copied to userspace
uninitialized.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>