Bluetooth: Fix SREJ_QUEUE corruption in L2CAP

Since all TxSeq values are modulo, we shall not compare them directly. We
have to compare their offset inside the TxWindow instead.

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