[iOS] Banner inconsistent behaviour when switching layouts

[maelig-moreau]

Steps to reproduce :

• iOS build
• Setup Portrait and Landscape layouts
• load and show banner ad on a position other than 1
• switch back and forth from Landscape to Portrait

The banner appear to be changing positions when switching layouts. Sometimes it looks like it is consistently occupying two different positions in Portrait and Landscape. Sometimes it might be in a certain position upon showing and when switching layout back and forth is shown at a different position on the same layout. Note that those positions might actually be out of the screen, making it look like they disappeared.

The bug doesn't occur at all on Android.