Wireguard support for Mullvad and Windscribe (#565)

- `internal/wireguard` client package with unit tests
- Implementation works with kernel space or user space if unavailable
- `WIREGUARD_PRIVATE_KEY`
- `WIREGUARD_ADDRESS`
- `WIREGUARD_PRESHARED_KEY`
- `WIREGUARD_PORT`
- `internal/netlink` package used by `internal/wireguard`

internal/models/connection.go

@@ -6,7 +6,7 @@ import (
 )
 
 type Connection struct {
-	// Type is the connection type and can be "openvpn"
+	// Type is the connection type and can be "openvpn" or "wireguard"
 	Type string `json:"type"`
 	// IP is the VPN server IP address.
 	IP net.IP `json:"ip"`
@@ -15,13 +15,17 @@ type Connection struct {
 	// Protocol can be "tcp" or "udp".
 	Protocol string `json:"protocol"`
 	// Hostname is used for IPVanish, IVPN, Privado
-	// and Windscribe for TLS verification
+	// and Windscribe for TLS verification.
 	Hostname string `json:"hostname"`
+	// PubKey is the public key of the VPN server,
+	// used only for Wireguard.
+	PubKey string `json:"pubkey"`
 }
 
 func (c *Connection) Equal(other Connection) bool {
 	return c.IP.Equal(other.IP) && c.Port == other.Port &&
-		c.Protocol == other.Protocol && c.Hostname == other.Hostname
+		c.Protocol == other.Protocol && c.Hostname == other.Hostname &&
+		c.PubKey == other.PubKey
 }
 
 func (c Connection) OpenVPNRemoteLine() (line string) {