allow awgtpman to run as unprivileged user

The awgtpman process is run as root only because it wants to bind to a
privileged port.  This is not necessary as capabilities exist to allow
running it as a unprivileged user:

* remove an unnecessary check in the awgtpman binary on the superuser
  status of the user

* set CAP_NET_BIND_SERVICE in the systemd service to allow it to bind
  to privileged port

This should allow the service to run as a non-privileged user, which we
set here to be advligorts.

closes #93

src/gds/awgtpman.c

@@ -175,12 +175,7 @@ CDS_HARDWARE cdsPciModules;
       initReflectiveMemory();
 #endif
       if (run_awg) {
-        if (geteuid() != 0) {
-	  printf ("Must be a superuser to run awgtpman\n");
-	  return 1;
-        } else {
-	  nice(-20);
-        }
+        nice(-20);
       }
 /*
                                 if ($::site =~ /^M/) {

support/systemd/rts-awgtpman@.service

@@ -5,5 +5,7 @@ Wants=rts-module@%i.service
 PartOf=rts@%i.target
 
 [Service]
+User=advligorts
+CapabilityBoundingSet=CAP_NET_BIND_SERVICE
 ExecStart=/usr/bin/rts_awgtpman_exec %i
 Restart=always