special case calls to get_address from the main pid.

This is prep work for moving syscalls/* away from directly using
page_rand and friends.
ioctl: don't use page_rand directly

using get_non_null_address gives more variation.
perf_event_open: don't use page_rand directly

using get_non_null_address gives more variation.
read: don't use page_rand directly

using get_non_null_address gives more variation.
TODO: come back to sendmsg later.
setsockopt: don't use page_rand directly

using get_non_null_address gives more variation.
write: don't use page_rand directly

using get_non_null_address gives more variation.