Config.uk: Imply LIBUKMMAP

Change `select LIBUKMMAP` to `imply LIBUKMMAP`. This is because
`LIBUKMMAP` may not be required for the Nginx build (and use
`LIBPOSIX_MMAP` instead).

With `select` in place you cannot disable `LIBUKMMAP`
resulting in a dependency erorr when enabling `LIBPOSIX_MMAP`.

With `imply` as a soft select, `LIBUKMMAP` can be disabled, removing the
dependency error.

Co-authored-by: Marc Rittinghaus <[email protected]>
Signed-off-by: Marc Rittinghaus <[email protected]>
Signed-off-by: Razvan Deaconescu <[email protected]>
Reviewed-by: Marc Rittinghaus <[email protected]>
Approved-by: Simon Kuenzer <[email protected]>
Tested-by: Unikraft CI <[email protected]>
GitHub-Closes: #15

Config.uk

@@ -8,7 +8,7 @@ menuconfig LIBNGINX
 	select LIBPOSIX_SYSINFO
 	select LIBPOSIX_SOCKET
 	select LIBPOSIX_EVENT
-	select LIBUKMMAP
+	imply LIBUKMMAP
 	select LIBUKTIME
 	select LIBUKSIGNAL
 	select LIBMUSL