main: fix return GL_FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL value

Return the proper value for two-dimensional array texture and three-dimensional
textures.

From OpenGL ES 3.0 spec, chapter 6.1.13 "Framebuffer Object Queries",
page 234:

"If pname is FRAMEBUFFER_ATTACHMENT_TEXTURE_LAYER and the texture
object named FRAMEBUFFER_ATTACHMENT_OBJECT_NAME is a layer of a
three-dimensional texture or a two-dimensional array texture, then params
will contain the number of the texture layer which contains the attached im-
age. Otherwise params will contain the value zero."

Furthermore, FRAMEBUFFER_ATTACHMENT_TEXTURE_LAYER is an alias of
FRAMEBUFFER_ATTACHMENT_TEXTURE_3D_ZOFFSET_EXT.

This patch fixes dEQP test:

dEQP-GLES3.functional.state_query.fbo.framebuffer_attachment_texture_layer

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>