Stop parsing rend protocol versions greater than 7 in legacy hidden service descriptors
REND_PROTOCOL_VERSION_BITMASK_WIDTH is 16, but rend_encode_v2_descriptors() only checks bits 0 to 7.
This was introduced in 0a6480c in 0.2.4.3-alpha, which fixed #6827 (moved), which was itself a bugfix on c58675 in 0.2.0.10-alpha.
I think we should wontfix this.