CURLINFO_ACTIVESOCKET.3: mention it replaces *LASTSOCKET

docs/libcurl/opts/CURLINFO_ACTIVESOCKET.3

@@ -35,6 +35,9 @@ returned. When you finish working with the socket, you must call
 \fIcurl_easy_cleanup(3)\fP as usual on the easy handle and let libcurl close
 the socket and cleanup other resources associated with the handle. This is
 typically used in combination with \fICURLOPT_CONNECT_ONLY(3)\fP.
+
+This option was added as a replacement for \fICURLINFO_LASTSOCKET(3)\fP since
+that one isn't working on all platforms.
 .SH PROTOCOLS
 All
 .SH EXAMPLE
@@ -45,4 +48,4 @@ Added in 7.45.0
 Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
 .SH "SEE ALSO"
 .BR curl_easy_getinfo "(3), " curl_easy_setopt "(3), "
-.BR CURLINFO_ACTIVESOCKET "(3), "
+.BR CURLINFO_LASTSOCKET "(3), "