mshv: Use kfree_rcu in mshv_portid_free

mshv: Use kfree_rcu in mshv_portid_free

mshv_portid_free() uses synchronize_rcu() followed by kfree() to
reclaim port table entries. This blocks the caller until a full RCU
grace period elapses, which is unnecessary since the same module already
uses the non-blocking kfree_rcu() pattern in mshv_port_table_fini().

Replace with kfree_rcu() to avoid the blocking wait and keep the
reclamation strategy consistent across the file.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>