Add socket receive buffer size configuration

[DineshI-MS]

Problem

The library currently doesn't provide a way to set the netlink socket receive buffer size. This causes ENOBUFS errors under moderate to high packet rates (>5k pps) with the default 208KB buffer.

Solution

This PR adds a new SockBufSize field to the Config struct that allows users to set the socket receive buffer size using SO_RCVBUFFORCE (with fallback to SO_RCVBUF).

Changes

• Added SockBufSize uint32 field to Config struct
• Modified Open() to apply the socket buffer size if specified
• Added tests to verify the functionality
• Updated documentation and examples

Testing

• Tested with various buffer sizes (0, 512KB, 2MB)
• Verified no regression when SockBufSize = 0 (default behavior)
• Confirmed ENOBUFS errors are eliminated with 2MB buffer at 10k+ pps

Backwards Compatibility

This change is fully backwards compatible:

• The zero value (0) maintains existing behavior
• No changes required for existing users
• Only users who need larger buffers need to set this field

[florianl]

@DineshI-MS Looking more at this approach. It might be easier to just provide an API to set the receiver buffer:

// SetReadBuffer SetReadBuffer sets the size of the receive buffer associated with this socket.
func (nflog *Nflog) SetReadBuffer(bytes int) error {
	return nflog.Con.SetReadBuffer(bytes)
}

This would redude the complexity of configuration and would also users allow to change it any time. Would you be open to update your PR with such an approach?

[DineshI-MS]

Thanks for providing this suggestion. I was able to set the buffer size this way without making any additional changes. I wasn’t aware of the API functions that are already part of netlink.Conn

  nf, err := nflog.Open(&config)
   if err != nil {
       return fmt.Errorf("failed to open nflog: %w", err)
   }
   defer nf.Close()

   reqSocketBufferSize := (512 * 1024) // set default as 512 KB

   if err := nf.Con.SetReadBuffer(reqSocketBufferSize); err != nil {
       return fmt.Errorf("failed to set read buffer: %w", err)
   }

[florianl]

@DineshI-MS Would you be open to update your PR with this new approach?

[florianl]

As Nflog already exposes *netlink.Conn, it might be best to just improve documentation. I might open a new PR in a few days improving documentation, if this PR becomes stale.

[florianl]

Closing as resolved with #54.