cxgb3: Restore dependency on INET

Commit ff33c0e1

 ('net: Remove bogus
dependencies on INET') wrongly removed this dependency.  cxgb3 uses
the arp_send() function defined in net/ipv4/arp.c.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>