net/tls: pass record number as a byte array

TLS offload code casts record number to a u64.  The buffer
should be aligned to 8 bytes, but its actually a __be64, and
the rest of the TLS code treats it as big int.  Make the
offload callbacks take a byte array, drivers can make the
choice to do the ugly cast if they want to.

Prepare for copying the record number onto the stack by
defining a constant for max size of the byte array.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>