Broadcast address calculation was broken in 2c99a44

[lestrrat]

The code here breaks broadcast address calculation, as applying the mask simply yields in the right most octet as 0.

Here's a fix. Let me know if you want me to create PR for it

diff --git a/discover.go b/discover.go
index 3ecd630..78ad5e6 100644
--- a/discover.go
+++ b/discover.go
@@ -1,6 +1,7 @@
 package main

 import (
+       "encoding/binary"
        "fmt"
        "log"
        "net"
@@ -95,8 +96,15 @@ func getBroadcastAddresses() ([]string, error) {
                        continue
                }
                for _, addr := range addrs {
-                       if n, ok := addr.(*net.IPNet); ok && !n.IP.IsLoopback() && n.IP.To4() != nil {
-                               baddrs = append(baddrs, n.IP.Mask(n.IP.DefaultMask()).String())
+                       if n, ok := addr.(*net.IPNet); ok && !n.IP.IsLoopback() {
+                               if v4addr := n.IP.To4(); v4addr != nil {
+                                       // convert all parts of the masked bits to its maximum value
+                                       // by converting the address into a 32 bit integer and then
+                                       // ORing it with the inverted mask
+                                       baddr := make(net.IP, len(v4addr))
+                                       binary.BigEndian.PutUint32(baddr, binary.BigEndian.Uint32(v4addr)|^binary.BigEndian.Uint32(n.IP.DefaultMask()))
+                                       baddrs = append(baddrs, baddr.String())
+                               }
                        }
                }
        }

PS: I'd also like to create a PR that removes duplicate broadcast addrs, if it's OK with you.

[macdylan]

LGTM, please create a PR, thank you.

[lestrrat]

@macdylan done: #12