As others have already confirmed, the original purpose of the ring was to serve as the attachment point for the magazine retainer.
The "Rifle, Short, Magazine Lee-Enfield" (SMLE) was introduced in 1903 to replace the "Rifle, Magazine Lee-Enfield" (MLE, commonly referred to as the "Long Lee") with a number of modifications arising from the insight and experience gained during the Boer War. The integral bolt cover was one of the features eliminated from the SMLE design ... but canvas action covers were not introduced until some 12 years later in mid-1915, as a partial response to the abominable trench warfare conditions being experienced in the Great War ...
I'd have to refer to my books to confirm if the ring on the front of the action remained through the intervening period, or if it was perhaps re-introduced to use for attaching the action cover.
The War Department "List of Changes" entry in 1915 which details the officially adopted action cover pattern specifically mentions that the covers are for use with the Ross rifle and Patten 1914 rifle also, IIRC.