Remove unnecessary defer

PiperOrigin-RevId: 214073949
Change-Id: I8fab916cd77362c13dac2c9dcf2ecc1710d87a5e

Author: iangudger

pkg/tcpip/transport/udp/endpoint.go

@@ -400,8 +400,8 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 
 	case tcpip.MulticastTTLOption:
 		e.mu.Lock()
-		defer e.mu.Unlock()
 		e.multicastTTL = uint8(v)
+		e.mu.Unlock()
 
 	case tcpip.AddMembershipOption:
 		nicID := v.NIC