net: fealnx: fix build for UML

On i386, when builtin (not a loadable module), the fealnx driver
inspects boot_cpu_data to see what CPU family it is running on, and
then acts on that data. The "family" struct member (x86) does not exist
when running on UML, so prevent that test and do the default action.

Prevents this build error on UML + i386:

../drivers/net/ethernet/fealnx.c: In function ‘netdev_open’:
../drivers/net/ethernet/fealnx.c:861:19: error: ‘struct cpuinfo_um’ has no member named ‘x86’

Fixes: 68f5d3f3 ("um: add PCI over virtio emulation driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-um@lists.infradead.org
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Link: https://lore.kernel.org/r/20211014050500.5620-1-rdunlap@infradead.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/fealnx.c

@@ -857,7 +857,7 @@ static int netdev_open(struct net_device *dev)
 	np->bcrvalue |= 0x04;	/* big-endian */
 #endif
 
-#if defined(__i386__) && !defined(MODULE)
+#if defined(__i386__) && !defined(MODULE) && !defined(CONFIG_UML)
 	if (boot_cpu_data.x86 <= 4)
 		np->crvalue = 0xa00;
 	else