tls: fix peeking with sync+async decryption

tls: fix peeking with sync+async decryption

If we peek from 2 records with a currently empty rx_list, and the
first record is decrypted synchronously but the second record is
decrypted async, the following happens:
  1. decrypt record 1 (sync)
  2. copy from record 1 to the userspace's msg
  3. queue the decrypted record to rx_list for future read(!PEEK)
  4. decrypt record 2 (async)
  5. queue record 2 to rx_list
  6. call process_rx_list to copy data from the 2nd record

We currently pass copied=0 as skip offset to process_rx_list, so we
end up copying once again from the first record. We should skip over
the data we've already copied.

Seen with selftest tls.12_aes_gcm.recv_peek_large_buf_mult_recs

Fixes: 692d7b5d1f91 ("tls: Fix recvmsg() to be able to peek across multiple records")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://lore.kernel.org/r/1b132d2b2b99296bfde54e8a67672d90d6d16e71.1709132643.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>