Bluetooth: Fix for GAP/SEC/SEM/BI-10-C

Security Mode 1 level 4, force us to use have key size 16 octects long.
This patch adds check for that.

This is required for the qualification test GAP/SEC/SEM/BI-10-C

Logs from test when ATT is configured with sec level BT_SECURITY_FIPS

< ACL Data TX: Handle 3585 flags 0x00 dlen 11                                                                       #28 [hci0] 3.785965
      SMP: Pairing Request (0x01) len 6
        IO capability: DisplayYesNo (0x01)
        OOB data: Authentication data not present (0x00)
        Authentication requirement: Bonding, MITM, SC, No Keypresses (0x0d)
        Max encryption key size: 16
        Initiator key distribution: EncKey Sign (0x05)
        Responder key distribution: EncKey IdKey Sign (0x07)
> ACL Data RX: Handle 3585 flags 0x02 dlen 11                                                                       #35 [hci0] 3.883020
      SMP: Pairing Response (0x02) len 6
        IO capability: DisplayYesNo (0x01)
        OOB data: Authentication data not present (0x00)
        Authentication requirement: Bonding, MITM, SC, No Keypresses (0x0d)
        Max encryption key size: 7
        Initiator key distribution: EncKey Sign (0x05)
        Responder key distribution: EncKey IdKey Sign (0x07)
< ACL Data TX: Handle 3585 flags 0x00 dlen 6                                                                        #36 [hci0] 3.883136
      SMP: Pairing Failed (0x05) len 1
        Reason: Encryption key size (0x06)
Signed-off-by: Łukasz Rymanowski <lukasz.rymanowski@codecoup.pl>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/smp.c

@@ -730,6 +730,10 @@ static u8 check_enc_key_size(struct l2cap_conn *conn, __u8 max_key_size)
 	struct hci_dev *hdev = conn->hcon->hdev;
 	struct smp_chan *smp = chan->data;
 
+	if (conn->hcon->pending_sec_level == BT_SECURITY_FIPS &&
+	    max_key_size != SMP_MAX_ENC_KEY_SIZE)
+		return SMP_ENC_KEY_SIZE;
+
 	if (max_key_size > hdev->le_max_key_size ||
 	    max_key_size < SMP_MIN_ENC_KEY_SIZE)
 		return SMP_ENC_KEY_SIZE;