* Updates to the netplay netpacket interface
- Switch environment call number from 76 to 78 (retire 76 as it was never used by any core)
- Simplify broadcasts by removing the option to send to all but one client
- Separate explicit flushing and querying of incoming packet into two operations (RETRO_NETPACKET_FLUSH_HINT and retro_netpacket_poll_receive_t)
- Enable a core to specify a protocol version string which can get used instead of core version to determine compatibility between two players
- Log and notify a separate message when there is a content crc mismsatch to convey it being less severe (as different games may be able to do network communication with each other)
* C89 compile fix