fix: usr: Fix update-policy grant external address passing

Only TCP client addresses are supposed to be passed to an `external` handler for the associated `update-policy` rule, but UDP client addresses were also being passed.  This could have caused the external handler to return a result it otherwise wouldn't. This has been fixed.

Closes #6061

Merge branch '6061-fix-grant-external-address-passing' into 'main'

See merge request isc-projects/bind9!12546