fix(config): skip check_filesystem_compatibility_on_host for ROOTFS_TYPE=nfs

ROOTFS_TYPE=nfs produces a rootfs tarball via `tar cp ... | gzip` in
rootfs-to-image.sh and never mounts NFS on the build host. The NFS
client runs on the target's kernel at boot time, so host-side NFS
filesystem support is irrelevant. Additionally, the check runs inside
the Armbian docker launcher where /lib/modules is empty, causing
`modprobe nfs` to fail even when the host kernel has nfs.ko available.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: iav

lib/functions/configuration/main-config.sh

@@ -160,8 +160,10 @@ function do_main_configuration() {
 			;;
 	esac
 
-	# Check if the filesystem type is supported by the build host
-	if [[ $CONFIG_DEFS_ONLY != yes ]]; then # don't waste time if only gathering config defs
+	# Check if the filesystem type is supported by the build host.
+	# Skipped for nfs: ROOTFS_TYPE=nfs produces a rootfs tarball;
+	# host-side filesystem support is irrelevant for the nfs case.
+	if [[ $CONFIG_DEFS_ONLY != yes && $ROOTFS_TYPE != nfs ]]; then
 		check_filesystem_compatibility_on_host
 	fi