net/tls: Remove VLA usage on nonce

It looks like the prior VLA removal, commit b16520f7 ("net/tls: Remove
VLA usage"), and a new VLA addition, commit c46234eb

 ("tls: RX path
for ktls"), passed in the night. This removes the newly added VLA, which
happens to have its bounds based on the same max value.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>