selftests: tls: add tls record_size_limit test

selftests: tls: add tls record_size_limit test

Test that outgoing plaintext records respect the tls TLS_TX_MAX_PAYLOAD_LEN
set using setsockopt(). The limit is set to be 128, thus, in all received
records, the plaintext must not exceed this amount.

Also test that setting a new record size limit whilst a pending open
record exists is handled correctly by discarding the request.

Suggested-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Link: https://patch.msgid.link/20251022001937.20155-2-wilfred.opensource@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>