Fix some minor record layer issues

Fix some minor record layer issues

Various comments referred to s->packet and s->packet_length instead of
s->rlayer.packet and s->rlayer.packet_length. Also fixed is a spot where
RECORD_LAYER_write_pending() should have been used. Based on the review
comments in #16077.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/16086)