Fixed missing field initializer warnings

Fixed `-Wmissing-field-initializers` warnings.
```
toxcore/DHT.c:1073: warning: missing initializer for field 'padding' of 'struct <anonymous>' [-Wmissing-field-initializers]
toxcore/LAN_discovery.c:147: warning: missing initializer for field 'padding' of 'struct <anonymous>' [-Wmissing-field-initializers]
toxcore/network.c:65: warning: missing initializer for field 'zeroes' of 'ADDR' [-Wmissing-field-initializers]
toxcore/network.c:210: warning: missing initializer for field 'zeroes' of 'ADDR' [-Wmissing-field-initializers]
```