sched/credit: avoid priority boost for capped domains when unpark

sched/credit: avoid priority boost for capped domains when unpark

When unpausing a capped domain, the scheduler currently clears the
CSCHED_FLAG_VCPU_PARKED flag before vcpu_wake(). This, in turn, causes the
vcpu_wake to set CSCHED_PRI_TS_BOOST, resulting in an unfair credit boost. The
comment around the changed lines already states that clearing the flag should
happen AFTER the unpause. This bug was introduced in commit be650750945
"credit1: Use atomic bit operations for the flags structure".

Original patch author credit: Xi Xiong while at Amazon.

Signed-off-by: Eslam Elnikety <elnikety@amazon.com>
Reviewed-by: Leonard Foerster <foersleo@amazon.de>
Reviewed-by: Petre Eftime <epetre@amazon.com>
Acked-by: Dario Faggioli <dfaggioli@suse.com>