### Description

Selected algorithm is a hash, over Call-ID, From, etc. If destination is not available, a new one must be selected, without breaking the hash assignation (all messages with the same hash must be forwarded to the same destination)

### Expected behavior

The load to the failed destination to be (hopefully) evenly distributed over the remaining destinations.

#### Actual observed behavior

All the messages that were supposed to be sent to the failed destination are sent to only one of the remaining, causing it to receive double load, comparing with the rest

#### Debugging Data

In this test, 6000 Calls were sent to a group of six destinations, using algorithm "0" (hash over Call-ID)

| All destinations active -- | -- Dest1 | 996 Dest2 | 997 Dest3 | 999 Dest4 | 1006 Dest5 | 1005 Dest6 | 997 Total | 6000


Repeating the test, but with destination Dest4 down:

| OriginalImplementation -- | -- Dest1 | 975 Dest2 | 993 Dest3 | 2022 Dest4 | 0 Dest5 | 1019 Dest6 | 991 Total | 6000


We can see that poor destination Dest3 receives double traffic

### Possible Solutions

I implemented a solution that does not break the expected behavior (messages with same hash are assigned the same destination, but with a better distribution over remaining destinations)

| New Implementation -- | -- Dest1 | 1175 Dest2 | 1206 Dest3 | 1191 Dest4 | 0 Dest5 | 1216 Dest6 | 1212 Total | 6000


Basically, the solution is as simple as to execute a rehash of the original hash.

I will create a pull request with the proposed change, which I already tested, as it can be seen on the previous chart.

### Additional Information

* **Kamailio Version**

``` kamailio 5.4.0-dev4 (x86_64/linux) 0c29e8-dirty ```

* **Operating System**:

``` Linux Rechitsa 5.4.19-100.fc30.x86_64 #1 SMP Tue Feb 11 22:27:11 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

```