tests: Fix regulatory domain reset in FST test case failure cases

tests: Fix regulatory domain reset in FST test case failure cases

send_iface_detach_request() can fail and that resulted in skipping a
call to restore_reg_domain() and leaving unexpected country
configuration for following test cases. This could result in failures,
e.g., in this sequence: fst_proto wpas_mesh_open_5ghz

Fix this by ignoring exceptions from send_iface_detach_request() and
continuing to restore regulatory domain.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>