floss: Fix discovery resume issue

CTSV Bluetooth LE Secure Client Test hangs because the discovery
request is not resumed properly which blocks the following GATT
connection.
This patch fixes the issue by clearing the is_discovery_paused flag
before calling start_discovery.

Bug: 284367921
Tag: #floss
Test: CTSV Bluetooth LE Secure Client Test on brya
Change-Id: I983fd7b65b22c4b9e577c629984c100dd3c09edb