sfc: add CONFIG_INET dependency for TC offload

sfc: add CONFIG_INET dependency for TC offload

The driver now fails to link when CONFIG_INET is disabled, so
add an explicit Kconfig dependency:

ld.lld: error: undefined symbol: ip_route_output_flow
>>> referenced by tc_encap_actions.c
>>>               drivers/net/ethernet/sfc/tc_encap_actions.o:(efx_tc_flower_create_encap_md) in archive vmlinux.a

ld.lld: error: undefined symbol: ip_send_check
>>> referenced by tc_encap_actions.c
>>>               drivers/net/ethernet/sfc/tc_encap_actions.o:(efx_gen_encap_header) in archive vmlinux.a
>>> referenced by tc_encap_actions.c
>>>               drivers/net/ethernet/sfc/tc_encap_actions.o:(efx_gen_encap_header) in archive vmlinux.a

ld.lld: error: undefined symbol: arp_tbl
>>> referenced by tc_encap_actions.c
>>>               drivers/net/ethernet/sfc/tc_encap_actions.o:(efx_tc_netevent_event) in archive vmlinux.a
>>> referenced by tc_encap_actions.c
>>>               drivers/net/ethernet/sfc/tc_encap_actions.o:(efx_tc_netevent_event) in archive vmlinux.a

Fixes: a1e82162af0b8 ("sfc: generate encap headers for TC offload")
Reviewed-by: Edward Cree <ecree.xilinx@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306151656.yttECVTP-lkp@intel.com/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230619091215.2731541-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>