rcutorture: Add full read-side contexts to "busted" torture type

rcutorture: Add full read-side contexts to "busted" torture type

The purpose of the "busted" torture type is to test rcutorture code paths
used only when a too-short grace period is detected.  Currently, "busted"
only uses normal rcu_read_lock()-style readers, which fails to exercise
much of the "Failure/close-call rcutorture reader segments" functionality.
This commit therefore sets the .extendables field of rcu_busted_ops to
RCUTORTURE_MAX_EXTEND in order to more fully exercise the reporting.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>