Correct signatures of context::current::peer_to_peer functions

[eyalroz]

The context::current::peer_to_peer namespace has the functions declarations:

void enable_access_to(const context_t &context, const context_t &peer_context);
void disable_access_to(const context_t &context, const context_t &peer_context);

... but we actually don't need the accessor context, and indeed, the definition doesn't have it. Embarrassing gaffe... let's fix it.