netfilter: nft_set_rbtree: overlap detection with element re-addition after deletion

This patch fixes spurious EEXIST errors.

Extend d2df92e9 ("netfilter: nft_set_rbtree: handle element
re-addition after deletion") to deal with elements with same end flags
in the same transation.

Reset the overlap flag as described by 7c84d414 ("netfilter:
nft_set_rbtree: Detect partial overlaps on insertion").

Fixes: 7c84d414 ("netfilter: nft_set_rbtree: Detect partial overlaps on insertion")
Fixes: d2df92e9

 ("netfilter: nft_set_rbtree: handle element re-addition after deletion")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>