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### Description

Currently the functions set_advertised_address and set_advertised_port only accept strings as parameters. Trying to use it with variable causes an error. Having the function using a hard coded value is not a good practice and in order to add flexibility to the script in different installations it would be nice to have this function accepting variables. Also, the 'advertise' option on the 'listen' parameter is not always desired because it apply for all messages sent via the socket, and there are situations where different advertised IP for the same interface are necessary.

### Expected behavior set_advertised_address should receive a variable as parameter and use its value to change the SIP headers.

### Actual observed behavior Kamailio won't start if set_advertised_address is used with a variable due to script parse error or it will set the SIP message with the literal string "$var(test)" for example, instead of using the value of $var(test).

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` # kamailio -v version: kamailio 5.2.2 (x86_64/linux) 67f967 flags: STATS: Off, USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MEM, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES ADAPTIVE_WAIT_LOOPS=1024, MAX_RECV_BUFFER_SIZE 262144 MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: 67f967 compiled on 11:40:41 Mar 11 2019 with gcc 4.8.5

```

* **Operating System**:

<!-- Details about the operating system, the type: Linux (e.g.,: Debian 8.4, Ubuntu 16.04, CentOS 7.1, ...), MacOS, xBSD, Solaris, ...; Kernel details (output of `uname -a`) -->

``` # uname -a Linux voice-conn-kamailio-1 3.10.0-514.21.2.el7.x86_64 #1 SMP Tue Jun 20 12:24:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

```