Check for timeout when trying reserved ports

rpc.Comm.Connect was trying to bind to 424 reserved ports, which is
overkill. Since nsock doesn't do an actual bind(2) call until
socket:connect for TCP, that meant up to 424 connect calls, each of
which is currently leaking a socket. This commit contains 3 fixes:

1. Add nmap.new_socket calls for non-privileged code path that were
moved inside the privileged loop to originally address the leak.

2. Check for TIMEOUT on each of the TCP connect calls and abandon the
Connect, avoiding many timeouts.

3. Try 10 random reserved ports (from 1 to 1024) instead of 400+.
Should be good odds of finding one unused, even when lots of threads are
trying (though empirical results would be helpful). Also, this should
reduce load since thread n won't need to fail n-1 bind attempts.

nselib/rpc.lua

@@ -166,27 +166,32 @@ Comm = {
       if ( port.protocol == "tcp" ) then
         if nmap.is_privileged() then
           -- Try to bind to a reserved port
-          for resvport = 600, 1024, 1 do
+          for i = 1, 10, 1 do
+            resvport = math.random(1, 1024)
             socket = nmap.new_socket()
             status, err = socket:bind(nil, resvport)
             if status then 
               status, err = socket:connect(host, port)
-              if status then break end
+              if status or err == "TIMEOUT" then break end
               socket:close()
             end
           end
         else
+          socket = nmap.new_socket()
           status, err = socket:connect(host, port)
         end
       else
         if nmap.is_privileged() then
           -- Try to bind to a reserved port
-          for resvport = 600, 1024, 1 do
+          for i = 1, 10, 1 do
+            resvport = math.random(1, 1024)
             socket = nmap.new_socket("udp")
             status, err = socket:bind(nil, resvport)
             if status then break end
             socket:close()
           end
+        else
+          socket = nmap.new_socket("udp")
         end
       end
       if (not(status)) then