chore(netlink): define own types with minimal fields

- Allow to swap `github.com/vishvananda/netlink`
- Allow to add build tags for each platform
- One step closer to development on non-Linux platforms

internal/netlink/conversion.go

@@ -0,0 +1,62 @@
+package netlink
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+)
+
+func netipPrefixToIPNet(prefix netip.Prefix) (ipNet *net.IPNet) {
+	if !prefix.IsValid() {
+		return nil
+	}
+
+	prefixAddr := prefix.Addr().Unmap()
+	ipMask := net.CIDRMask(prefix.Bits(), prefixAddr.BitLen())
+	ip := netipAddrToNetIP(prefixAddr)
+
+	return &net.IPNet{
+		IP:   ip,
+		Mask: ipMask,
+	}
+}
+
+func netIPNetToNetipPrefix(ipNet *net.IPNet) (prefix netip.Prefix) {
+	if ipNet == nil || (len(ipNet.IP) != net.IPv4len && len(ipNet.IP) != net.IPv6len) {
+		return prefix
+	}
+
+	var ip netip.Addr
+	if ipv4 := ipNet.IP.To4(); ipv4 != nil {
+		ip = netip.AddrFrom4([4]byte(ipv4))
+	} else {
+		ip = netip.AddrFrom16([16]byte(ipNet.IP))
+	}
+	bits, _ := ipNet.Mask.Size()
+	return netip.PrefixFrom(ip, bits)
+}
+
+func netipAddrToNetIP(address netip.Addr) (ip net.IP) {
+	switch {
+	case !address.IsValid():
+		return nil
+	case address.Is4() || address.Is4In6():
+		bytes := address.As4()
+		return net.IP(bytes[:])
+	default:
+		bytes := address.As16()
+		return net.IP(bytes[:])
+	}
+}
+
+func netIPToNetipAddress(ip net.IP) (address netip.Addr) {
+	if len(ip) != net.IPv4len && len(ip) != net.IPv6len {
+		return address // invalid
+	}
+
+	address, ok := netip.AddrFromSlice(ip)
+	if !ok {
+		panic(fmt.Sprintf("converting %#v to netip.Addr failed", ip))
+	}
+	return address.Unmap()
+}