[#33] network: Implement tool to work with local address

Implement read-only local network address source. Implement function for
check if network address is local.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/network/address.go

@@ -12,6 +12,12 @@ type Address struct {
 	ma multiaddr.Multiaddr
 }
 
+// LocalAddressSource is an interface of local
+// network address container with read access.
+type LocalAddressSource interface {
+	LocalAddress() *Address
+}
+
 func (a Address) String() string {
 	return a.ma.String()
 }
@@ -37,3 +43,9 @@ func AddressFromString(s string) (*Address, error) {
 		ma: ma,
 	}, nil
 }
+
+// IsLocalAddress returns true if network endpoint from local address
+// source is equal to network endpoint of passed address.
+func IsLocalAddress(src LocalAddressSource, addr *Address) bool {
+	return src.LocalAddress().NetAddr() == addr.NetAddr()
+}