nginx: bump to 1.21.1 and improve makefile

- Bump to 1.21.1
- Rework makefile to fix bad make refresh
- Refresh patch

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>

net/nginx/patches/dav-nginx/100-drop-libxslt-dep.patch

@@ -0,0 +1,14 @@
+--- a/nginx-dav-ext-module/config
++++ b/nginx-dav-ext-module/config
+@@ -8,9 +8,8 @@ ngx_module_name=ngx_http_dav_ext_module
+ # building nginx with the xslt module, in which case libxslt will
+ # be linked anyway.  In other cases libxslt is just redundant.
+ # If that's a big deal, libxml2 can be linked directly:
+-# ngx_module_libs=-lxml2
+-
+-ngx_module_libs=LIBXSLT
++ngx_module_libs=-lxml2
++ngx_module_incs=$(pkg-config --cflags-only-I libxml-2.0 | sed 's/^-I//')
+ 
+ ngx_module_srcs="$ngx_addon_dir/ngx_http_dav_ext_module.c"
+