Use fprintf(stderr) instead of gctl_error() to print a warning about too

big sector size. When gctl error is set gctl_has_param() always returns
'false', which prevents geli(8) from finding some arguments and also masks
an error, which is generates in such case.

MFC after:	3 days

sbin/geom/class/eli/geom_eli.c

@@ -749,8 +749,8 @@ eli_init(struct gctl_req *req)
 			return;
 		}
 		if (val > sysconf(_SC_PAGE_SIZE)) {
-			gctl_error(req, "warning: Using sectorsize bigger than "
-			    "the page size!");
+			fprintf(stderr,
+			    "warning: Using sectorsize bigger than the page size!\n");
 		}
 		md.md_sectorsize = val;
 	}