package/strace: disable bpf support for m68k

Mismatch in struct bpf_prog_info fields offset between kernel headers
and strace local definition causes build failure. Disable bpf support
for m68k until upstream (either strace or the kernel) find a solution.

https://lists.strace.io/pipermail/strace-devel/2019-May/thread.html#8750

Fixes:
http://autobuild.buildroot.net/results/c036b11bf1f2fc39f42661634ef3e03360fb85de/
http://autobuild.buildroot.net/results/f142e4c7f0d512bb872572f5e678230117ab0ad5/
http://autobuild.buildroot.net/results/b74a17cfa7112c026938cacafdd18c6dca285005/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>