P2P: Fix 32-bit compiler warnings on service discovery reference

P2P: Fix 32-bit compiler warnings on service discovery reference

Convert core wpa_supplicant code to use u64 instead of void * for the
P2P service discovery reference. Use uintptr_t in type casts in
p2p_supplicant.c to handle the conversion without warnings.

Note: This needs to be revisited for 128-bit CPU where sizeof(void *)
could be larger than sizeof(u64).

Signed-hostap: Jouni Malinen <j@w1.fi>