ksmbd: resolve symlinks in share paths before writing ksmbd.conf

[ispyisail]

ksmbd's kernel module returns NT_STATUS_ACCESS_DENIED when a share
root path is a symlink. The "Same Partition On Any USB Drive" option
in the USB Storage page stores the dev-based symlink path
(e.g. /tmp/usb_mount/dev_sda1) rather than the UUID-based real path,
causing all shares configured with that option to be inaccessible.

Confirmed on hardware: connecting via smbclient to a share with a
symlink root returns NT_STATUS_ACCESS_DENIED; resolving the path
first gives a successful directory listing.

Add readlink -f in smb_add_share after reading the path from UCI
so ksmbd always receives a real directory path. The fallback || echo "$path"
preserves the original path if the target does not yet exist (drive
not plugged in).

[ispyisail]

The readlink -f "$path" 2>/dev/null || echo "$path" pattern is correct — it resolves symlinks, suppresses errors when the path does not exist yet (e.g. drive not yet mounted at init time), and falls back to the original path safely.

One bug introduced: the diff includes a file mode change on ksmbd.init from 100755 → 100644. Init scripts need to be executable or service ksmbd start/stop/restart and procd invocations break. This looks like a local core.fileMode mismatch rather than an intentional change.

Fixed in the branch with git update-index --chmod=+x.