refactor: protect => quic.sockopts

Android's VpnService.protect() itself is confusing, so we rename the
"protect" feature with the name `fdControlUnixSocket` and make it a
sub-option under `quic.sockopts`.

A unit test is added to make sure the protect feature works.

I also added two other common options to `quic.sockopts` that I copied
from my other projects but did not fully test here.

extras/transport/udphop/conn.go

@@ -7,8 +7,6 @@ import (
 	"sync"
 	"syscall"
 	"time"
-
-	"github.com/apernet/hysteria/extras/protect"
 )
 
 const (
@@ -22,7 +20,7 @@ type udpHopPacketConn struct {
 	Addr          net.Addr
 	Addrs         []net.Addr
 	HopInterval   time.Duration
-	ListenUDPFunc protect.ListenUDPFunc
+	ListenUDPFunc ListenUDPFunc
 
 	connMutex   sync.RWMutex
 	prevConn    net.PacketConn
@@ -46,7 +44,9 @@ type udpPacket struct {
 	Err  error
 }
 
-func NewUDPHopPacketConn(addr *UDPHopAddr, hopInterval time.Duration, listenUDPFunc protect.ListenUDPFunc) (net.PacketConn, error) {
+type ListenUDPFunc = func() (net.PacketConn, error)
+
+func NewUDPHopPacketConn(addr *UDPHopAddr, hopInterval time.Duration, listenUDPFunc ListenUDPFunc) (net.PacketConn, error) {
 	if hopInterval == 0 {
 		hopInterval = defaultHopInterval
 	} else if hopInterval < 5*time.Second {