linux: bump the default version from 3.10.0 to 3.17.0

This is required for Qt5, as found in Ubuntu Focal.  The library contains
the minimum kernel version encoded in an ELF note; this makes rtld ignore
it altogether, with a confusing error message.  Without it, things fail
like this:

$ konsole: error while loading shared libraries: libQt5Core.so.5: cannot
open shared object file: No such file or directory

For reference, the Qt kernel version requirements can be found at:
https://github.com/qt/qtbase/blob/dev/src/corelib/global/minimum-linux_p.h

Sponsored by:	The FreeBSD Foundation
Reviewed By:	emaste
Differential Revision:	https://reviews.freebsd.org/D28105

sys/compat/linux/linux_mib.h

@@ -47,7 +47,7 @@ int	linux_get_oss_version(struct thread *td);
 int	linux_kernver(struct thread *td);
 
 #define	LINUX_KVERSION		3
-#define	LINUX_KPATCHLEVEL	10
+#define	LINUX_KPATCHLEVEL	17
 #define	LINUX_KSUBLEVEL		0
 
 #define	LINUX_KERNVER(a,b,c)	(((a) << 16) + ((b) << 8) + (c))