Filter Wizard: simplify condition settings when advanced is enabled

Signed-off-by: Tim Harder <timothy.harder@analog.com>
libiio: only load library is it's not loaded already

This stops matlab from complaining about the library class already
existing after it's loaded previously.

Signed-off-by: Tim Harder <timothy.harder@analog.com>
Filter Wizard: minor variable usage simplification

Signed-off-by: Tim Harder <timothy.harder@analog.com>
Filter Wizard: try to fix advanced toggling and fcutoff settings

Filters saved with advanced mode enabled (with various extra settings
like fcutoff and phase equalization potentially different then
non-advanced filters) should be reloaded with advanced mode enabled.
Previously this was broken during some logic cleanup.

There still appears to be a bug where toggling the advanced settings
option for one of the preconfigured LTE filters changes the fcutoff
setting; however, this might have to do with manually calculating
different values than what the get_caldiv function returns.

Signed-off-by: Tim Harder <timothy.harder@analog.com>