memory: Make operations using MemoryRegionIoeventfd struct pass by pointer.

memory: Make operations using MemoryRegionIoeventfd struct pass by pointer.

This changes the functions memory_region_ioeventfd_equal, memory_region_ioeventfd_before, and their callers,
to pass the MemoryRegionIoeventfd struct via pointer, instead of directly passing the struct. This saves on stack space
and is considered safe practice.

Signed-off-by: Tristan Burgess <tburgessdev@gmail.com>
Message-Id: <20180529030445.177867-1-tburgessdev@gmail.com>
Fixes: Launchpad bug 1720969
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>