tls: Fix tls_sw_sendmsg error handling

We've noticed that NFS can hang when using RPC over TLS on an unstable
connection, and investigation shows that the RPC layer is stuck in a tight
loop attempting to transmit, but forever getting -EBADMSG back from the
underlying network. The loop begins when tcp_sendmsg_locked() returns
-EPIPE to tls_tx_records(), but that error is converted to -EBADMSG when
calling the socket's error reporting handler.

Instead of converting errors from tcp_sendmsg_locked(), let's pass them
along in this path. The RPC layer handles -EPIPE by reconnecting the
transport, which prevents the endless attempts to transmit on a broken
connection.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Fixes: a42055e8d2c3 ("net/tls: Add support for async encryption of records for performance")
Link: https://patch.msgid.link/9594185559881679d81f071b181a10eb07cd079f.1736004079.git.bcodding@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>