Add function to perform an alive test and get the amount of alive hosts.

[jjnicola]

What:
Add function to perform an alive test and get the amount of alive hosts.

Why:
There were just to ways to perform an alive scan, either using the client in which the results are printed in the stdout, or using the functions from the library which requires a redis kb and set preferences.
This function it is an hybrid between the both methods, which does not requires a kb, takes the preferences (port, alive test method) from prefs and which just return the amount of alive hosts.

How:
A small c program using the function:

sudo ./boreas_heartbeat 192.168.0.227

#include <glib.h>
#include <gvm/base/prefs.h> /* for prefs_get() */
#include <gvm/boreas/hostalivedetection.h>

void
main(int argc, char **argv)
{
  int alive = 0;
  boreas_error_t alive_test_err;
  
  prefs_set("ALIVE_TEST", "2");
  prefs_set("port_range", "80,137,587,3128,8081");

  alive_test_err = is_host_alive(argv[1], &alive);
  if (alive_test_err == NO_ERROR && alive > 0)
    g_message("Host %s alive", argv[1]);
  else
    g_message("Host %s dead", argv[1]);
 
}

Checklist:

• Tests
• CHANGELOG Entry