tls: splice_read: fix accessing pre-processed records

tls: splice_read: fix accessing pre-processed records

BugLink: https://bugs.launchpad.net/bugs/1953370
[ Upstream commit e062fe99cccd9ff9f232e593d163ecabd244fae8 ]

recvmsg() will put peek()ed and partially read records onto the rx_list.
splice_read() needs to consult that list otherwise it may miss data.
Align with recvmsg() and also put partially-read records onto rx_list.
tls_sw_advance_skb() is pretty pointless now and will be removed in
net-next.

Fixes: 692d7b5d1f91 ("tls: Fix recvmsg() to be able to peek across multiple records")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>