Update capture_opts in extcap_cleanup().

This fixes redundant extcap_pid handle close that could occur in
capture_opts_del_iface() which resulted in unhandled exception on
Windows.

Change-Id: I06b680fcb65cd6fd854a25fb1b01248dce3251a1
Reviewed-on: https://code.wireshark.org/review/4447
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>