net: tls: fix silent data drop under pipe back-pressure

net: tls: fix silent data drop under pipe back-pressure

tls_sw_splice_read() uses len when advancing rxm->offset / rxm->full_len
after skb_splice_bits(), rather than copied (the actual number of bytes
successfully spliced into the pipe). When the destination pipe cannot
accept all the requested bytes, splice_to_pipe() returns fewer bytes
than len, and 'len - copied' of data is effectively skipped over.

Fixes: e062fe99cccd ("tls: splice_read: fix accessing pre-processed records")
Link: https://patch.msgid.link/20260429222944.2139041-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>