if_bridge: Remove unused disable parameter in bridge_stop

The `int disable``` parameter is included in the bridge_stop function
signature but is not used in the function body.

I had noticed this when tracing the driver's path while learning more
about the ifnet library.

This parameter originally appeared when importing the driver from NetBSD.
However, the FreeBSD ifnet library no longer requires an if_stop function.
Meaning that the function signature can be changed to only contain needed
parameters for our bridge driver.

Discussed with: freebsd-net@ mailing list
Signed-off-by: Acesp25 <acesp25@freebsd.org>
Reviewed by: kp
Pull-Request: https://github.com/freebsd/freebsd-src/pull/2290