[NSOCK] Sandwitched pcap_read_on_nonselect() statements between #ifndef

PCAP_CAN_DO_SELECT guards to prevent them from being executed on systems that
actually provide selectable pcap descriptors.

nsock/src/engine_select.c

@@ -126,8 +126,10 @@ void process_event(mspool *nsp, gh_list *evlist, msevent *nse, int ev);
 void process_iod_events(mspool *nsp, msiod *nsi, int ev);
 
 #if HAVE_PCAP
+#ifndef PCAP_CAN_DO_SELECT
 int pcap_read_on_nonselect(mspool *nsp);
 #endif
+#endif
 
 /* defined in nsock_event.c */
 void update_first_events(msevent *nse);
@@ -315,11 +317,13 @@ int select_loop(mspool *nsp, int msec_timeout) {
     }
 
 #if HAVE_PCAP
+#ifndef PCAP_CAN_DO_SELECT
     /* do non-blocking read on pcap devices that doesn't support select()
      * If there is anything read, just leave this loop. */
     if (pcap_read_on_nonselect(nsp)) {
       /* okay, something was read. */
     } else
+#endif
 #endif
     {
       /* Set up the descriptors for select */