bnxt_en: Free context memory in the open path if firmware has been reset.

This will trigger new context memory to be rediscovered and allocated
during the re-probe process after a firmware reset.  Without this, the
newly reset firmware does not have valid context memory and the driver
will eventually fail to allocate some resources.

Fixes: ec5d31e3

 ("bnxt_en: Handle firmware reset status during IF_UP.")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>