Bluetooth: Tweaks to l2cap_send_i_or_rr_or_rnr() flow

l2cap_send_sframe() already set the F-bit if we set L2CAP_CONN_SEND_FBIT
and unset L2CAP_CONN_SEND_FBIT after send the F-bit.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>