Blocking creatures with menace and an equipment giving 'can only be blocked by one creature'
Both abilities are active (and Vorrac Battlehorns' ability doesn't 'trigger', it is always in effect).


  509.1b The defending player checks each creature they control to see whether it's affected by any restrictions (effects that say a creature can't block, or that it can't block unless some condition is met). If any restrictions are being disobeyed, the declaration of blockers is illegal.


Your opponent won't be able to block the creature with the Vorrac Battlehorns, since it can't be blocked by more than one creature (due to the equipment) and it can't be blocked by less than two creatures (due to the Wolf). Both are restrictions and the rules above state they must be obeyed. Note that they are free to block the Wolf or not, but need at least two creatures to do so.

Incidentally, this means a Pyreheart Wolf equipped with Vorrac Battlehorns is unblockable.