net: thunderx: Wait for delayed work to finish before destroying it

While VNIC or BGX driver teardown, wait for already scheduled delayed work to
finish before destroying it.

Signed-off-by: Thanneeru Srinivasulu <tsrinivasulu@caviumnetworks.com>
Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>