cxgb4/cxgb4vf: Fix mac_hlist initialization and free

Null pointer dereference seen when cxgb4vf driver is unloaded
without bringing up any interfaces, moving mac_hlist initialization
to driver probe and free the mac_hlist in remove to fix the issue.

Fixes: 24357e06 ("cxgb4vf: fix memleak in mac_hlist initialization")
Signed-off-by: Arjun Vynipadath <arjun@chelsio.com>
Signed-off-by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>