net/tls: remove false positive warning

It's possible that TCP stack will decide to retransmit a packet
right when that packet's data gets acked, especially in presence
of packet reordering.  This means that packets may be in flight,
even though tls_device code has already freed their record state.
Make fill_sg_in() and in turn tls_sw_fallback() not generate a
warning in that case, and quietly proceed to drop such frames.

Make the exit path from tls_sw_fallback() drop monitor friendly,
for users to be able to troubleshoot dropped retransmissions.

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>