Misc sockets, crypto and VNC fixes * Fix rare EADDRINUSE failures on OpenBSD platforms seen with migration * Fix & test overwriting of hash output buffer * Close connection instead of returning empty SASL mechlist to VNC clients * Fix handling of SASL SSF on VNC server UNIX sockets * Fix handling of NULL SASL server data in VNC server * Validate trailing NUL padding byte from SASL client * Fix & test AF_ALG crypto backend build * Remove unused code in sockets and crypto subsystems