fiber: don't skip fiber_obj:info() arguments

Commit b18dd47f ("Introduce backtrace=true option to fiber.info()")
introduced a way to skip backtraces in fiber.info() calls.
Commit 9da7e03e ("fiber: introduce fiber_o:info() and fiber_o:csw()")
introduced `options` function for fiber object however it ignored
passed options.
This patch fixed it. Currently fiber:info({backtrace = false})
returns info without backtrace.

Closes #7210

NO_DOC=bugfix

(cherry picked from commit 0eac13b9)