fake_trx/udp_link.py: set SO_REUSEADDR socket option

Setting this option allows one to reuse existing connections,
for example, by injecting CTRL commands or DATA bursts into
existing connections between fake_trx.py and trxcon.

Change-Id: I0882c76affa9a668a12d10967081054d2b666ed1

src/target/fake_trx/udp_link.py

@@ -27,6 +27,7 @@ import socket
 class UDPLink:
 	def __init__(self, remote_addr, remote_port, bind_port):
 		self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+		self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
 		self.sock.bind(('0.0.0.0', bind_port))
 		self.sock.setblocking(0)