Add option to reinitialize call media transports

[ming]

The ticket will add pjsua_call_flag PJSUA_CALL_REINIT_MEDIA, which will deinitialize and recreate media, including media transport. It is useful in IP address change situation, if the media transport address (or address family) changes, for example during IPv4/IPv6 network handover.

To use this feature, call the API pjsua_call_reinvite()/reinvite2(), or pjsua_call_update()/update2(). The only drawback of using this option is that if the re-INVITE/UPDATE fails, the old media will not be reverted.

[ming]

In 5490:

Fixed #1982: Add option to reinitialize call media transports

[ming]

In 5491:

Re #1982: Add the new call flag for PJSUA2 swig

[ming]

In 5492:

Re #1982: Cleanup call setting flags even if callbacks on_call_tx/rx_offer() not implemented
Otherwise this could cause media to be unintentionally reinitialized on re-INVITEs/updates.
Refer to ticket #1793.