doc/man3/SSL_poll.pod: mention SSL_POLL_EVENT_{EL,IC} in SYNOPSIS

doc/man3/SSL_poll.pod: mention SSL_POLL_EVENT_{EL,IC} in SYNOPSIS

While the constants are present since the initial commit 2a5ee0a08d2c "QUIC:
Add polling API", they weren't initially documented in c9b0df2250e2 "QUIC:
Add manpage for SSL_poll" (probably due to absence of the QUIC server
mode support at the time), and mentioned for the first time in b20f55702100
"QUIC: Update SSL_poll documentation", but without the accompanying update
of the SYNOPSIS section.  Rescind the omission by updating it as well.

Complements: b20f55702100 "QUIC: Update SSL_poll documentation"
Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Paul Yang <paulyang.inf@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28303)