tcp_connect_bind binds to a local address before connecting.

Set laddr and laddr6 with http_client_set_laddr, http_client_set_laddr6
to bind http requests to a local ip address.

http_request selects between laddr and laddr6 after the address family
of the server address was detected.

Cisco phones send periodic REGISTER with Expires 0 to the SIP proxy.

After a registration failure a new instance of sipreg is allocated in order to
send periodic Cisco REGISTER keep-alives. These keep-alives will detect when
the SIP proxy becomes available again. The new function can be used to
initialize failc, thus sipreg_failed() returns true initially.

Each digest challenge for a REGISTER should start without authorization header.
This applies to periodic re-registration, for de-registration and also to
Cisco REGISTER keep-alives.

The Cisco REGISTER keep-alives detect that a SIP proxy becomes available again.
This has to be reported to the response handler in baresip.

Alfred's sip websocket patch

main: fix windows file descriptors #20

Co-authored-by: jjj <john.juul.jensen@hotmail.com>