drivers/net: netdevsim depends on INET

If CONFIG_INET is not set and CONFIG_NETDEVSIM=y.
Building drivers/net/netdevsim/fib.o will get the following error:

drivers/net/netdevsim/fib.o: In function `nsim_fib4_rt_hw_flags_set':
fib.c:(.text+0x12b): undefined reference to `fib_alias_hw_flags_set'
drivers/net/netdevsim/fib.o: In function `nsim_fib4_rt_destroy':
fib.c:(.text+0xb11): undefined reference to `free_fib_info'

Correct the Kconfig for netdevsim.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 48bb9eb4 ("netdevsim: fib: Add dummy implementation for FIB offload")
Signed-off-by: Hongbo Yao <yaohongbo@huawei.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>