sysutil: fix binding capability defining

internal/sysutil/os_linux.go

@@ -12,7 +12,10 @@ import (
 
 func canBindPrivilegedPorts() (can bool, err error) {
 	cnbs, err := unix.PrctlRetInt(unix.PR_CAP_AMBIENT, unix.PR_CAP_AMBIENT_IS_SET, unix.CAP_NET_BIND_SERVICE, 0, 0)
-	return cnbs == 1, err
+	// Don't check the error because it's always nil on Linux.
+	adm, _ := haveAdminRights()
+
+	return cnbs == 1 || adm, err
 }
 
 func setRlimit(val uint) {
@@ -26,6 +29,8 @@ func setRlimit(val uint) {
 }
 
 func haveAdminRights() (bool, error) {
+	// The error is nil because the platform-independent function signature
+	// requires returning an error.
 	return os.Getuid() == 0, nil
 }