Added clarifying comment

src/tcp_address.cpp

@@ -413,7 +413,7 @@ int zmq::tcp_address_t::resolve (const char *name_, bool local_, bool ipv6_, boo
     std::string addr_str (name_, delimiter - name_);
     std::string port_str (delimiter + 1);
 
-    //  Remove square brackets around the address, if any.
+    //  Remove square brackets around the address, if any, as used in IPv6
     if (addr_str.size () >= 2 && addr_str [0] == '[' &&
           addr_str [addr_str.size () - 1] == ']')
         addr_str = addr_str.substr (1, addr_str.size () - 2);