Fix udp:setpeername("*")

There seems to be a curious difference between MacOS and
Linux and I am not sure if this is documented. When you
break a "connection" on Mac OS, you only eliminate the peer
association, but the local address remains bound. On Linux,
breaking a "connection" eliminates the binding to the local
address. Have you guys ever come accross this?

Another irritating difference is that connect() returns the
error EAFNOSUPPORT on Mac OS. I am going to ignore all
errors when the reason for calling connect() is simply to
break the "connection".

test/udpconnectclnt.lua

@@ -0,0 +1,19 @@
+local socket = require"socket"
+local udp = socket.udp
+local localhost = "127.0.0.1"
+local port = arg[1]
+
+se = udp(); se:setoption("reuseaddr", true)
+se:setsockname(localhost, 5062)
+print("se", se:getsockname())
+sc = udp(); sc:setoption("reuseaddr", true)
+sc:setsockname(localhost, 5061)
+print("sc", sc:getsockname())
+
+se:sendto("this is a test from se", localhost, port)
+socket.sleep(1)
+sc:sendto("this is a test from sc", localhost, port)
+socket.sleep(1)
+se:sendto("this is a test from se", localhost, port)
+socket.sleep(1)
+sc:sendto("this is a test from sc", localhost, port)

test/udpconnectsrvr.lua

@@ -0,0 +1,16 @@
+local socket = require"socket"
+local udp = socket.udp
+local localhost = "127.0.0.1"
+local s = assert(udp())
+assert(tostring(s):find("udp{unconnected}"))
+print("setpeername", s:setpeername(localhost, 5061))
+print("getsockname", s:getsockname())
+assert(tostring(s):find("udp{connected}"))
+print(s:receive())
+print("setpeername", s:setpeername("*"))
+print("getsockname", s:getsockname())
+s:sendto("a", localhost, 12345)
+print("getsockname", s:getsockname())
+assert(tostring(s):find("udp{unconnected}"))
+print(s:receivefrom())
+s:close()