net: phy: mscc: fix macsec key length

The key length used to store the macsec key was set to MACSEC_KEYID_LEN
(16), which is an issue as:
- This was never meant to be the key length.
- The key length can be > 16.

Fix this by using MACSEC_MAX_KEY_LEN instead (the max length accepted in
uAPI).

Fixes: 28c5107a ("net: phy: mscc: macsec support")
Reported-by: NLior Nahmanson <liorna@nvidia.com>
Signed-off-by: NAntoine Tenart <atenart@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/phy/mscc/mscc_macsec.c

@@ -501,7 +501,7 @@ static u32 vsc8584_macsec_flow_context_id(struct macsec_flow *flow)
 }
 
 /* Derive the AES key to get a key for the hash autentication */
-static int vsc8584_macsec_derive_key(const u8 key[MACSEC_KEYID_LEN],
+static int vsc8584_macsec_derive_key(const u8 key[MACSEC_MAX_KEY_LEN],
 				     u16 key_len, u8 hkey[16])
 {
 	const u8 input[AES_BLOCK_SIZE] = {0};

drivers/net/phy/mscc/mscc_macsec.h

@@ -81,7 +81,7 @@ struct macsec_flow {
 	/* Highest takes precedence [0..15] */
 	u8 priority;
 
-	u8 key[MACSEC_KEYID_LEN];
+	u8 key[MACSEC_MAX_KEY_LEN];
 
 	union {
 		struct macsec_rx_sa *rx_sa;