intervals: set internal element location with the deletion trigger

intervals: set internal element location with the deletion trigger

set location of internal elements (already in the kernel) to the one
that partial or fully deletes it.

Otherwise, error reporting refers to internal location.

Before this patch:

 # nft delete element x y { 1.1.1.3 }
 Error: Could not process rule: Too many open files in system
 delete element x y { 1.1.1.3 }
                      ^^^^^^^

After this patch:

 # nft delete element x y { 1.1.1.3 }
 Error: Could not process rule: Too many open files in system
 delete element x y { 1.1.1.3 }
                      ^^^^^^^

This occurs after splitting an existing interval in two:

 remove: [1010100-10101ff]
 add: [1010100-1010102]
 add: [1010104-10101ff]

which results in two additions after removing the existing interval
that is split.

Fixes: 81e36530fcac ("src: replace interval segment tree overlap and automerge")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>