gve: Fix memory leak during reset

Before this change, during reset we were allocating new memory for
priv->ptype_lut_dqo, irq_db_array and the counter_array over the old
memory. This change ensures we do not allocate new memory during reset
and avoid memory leaks.

Signed-off-by: Vee Agarwal <veethebee@google.com>
Signed-off-by: Jasper Tran O'Leary <jtranoleary@google.com>

Reviewed by: delphij, markj
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D48970