change SNMP to be a cached transport singleton

lib/App/Netdisco/Backend/Worker/Interactive/DeviceActions.pm

@@ -1,6 +1,6 @@
 package App::Netdisco::Backend::Worker::Interactive::DeviceActions;
 
-use App::Netdisco::Util::SNMP 'snmp_connect_rw';
+use App::Netdisco::Core::Transport::SNMP;
 use App::Netdisco::Util::Device 'get_device';
 use App::Netdisco::Backend::Util ':all';
 
@@ -22,7 +22,7 @@ sub _set_device_generic {
   $data ||= '';
 
   # snmp connect using rw community
-  my $info = snmp_connect_rw($ip)
+  my $info = App::Netdisco::Core::Transport::SNMP->instance->writer_for($ip)
     or return job_defer("Failed to connect to device [$ip] to update $slot");
 
   my $method = 'set_'. $slot;