Use SNMP profiles' own snmp_version property

`ManagementProfile.snmp_version` already does the heavy lifting for
us when it comes to parse the SNMP version value of an SNMP profile,
so let's use that instead to avoid issues like the one described in
#2767

python/nav/ipdevpoll/snmp/common.py

@@ -204,13 +204,11 @@ def factory(
         if netbox:
             profile = netbox.get_preferred_snmp_management_profile()
             if profile:
-                if profile.protocol == profile.PROTOCOL_SNMPV3:
-                    kwargs["version"] = 3
                 kwargs_out.update(
                     {k: v for k, v in profile.configuration.items() if hasattr(cls, k)}
                 )
-                # Sometimes profiles store the version number as a string
-                kwargs_out["version"] = int(kwargs_out["version"])
+                # Let profile object parse its own version to an int
+                kwargs_out["version"] = profile.snmp_version
             else:
                 _logger.debug("%r has no snmp profile", netbox)
                 return None