cxgb4: Force cxgb4 driver as MASTER in kdump kernel

When is_kdump_kernel() is true, Forcing cxgb4 driver as Master so we can
reinitialize the Firmware/Chip. Also reduce memory usage by disabling
offload.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>