Fixes SEGFAUL in libbcc when actually setting a lost_cb
Fixes SEGFAUL in libbcc when actually setting a lost_cb

When setting a lost_cb, the reference to the ctypes function is not retained like the regular callback,
this leads to a SEGFAULT if the gc kills the lost_fn if a lost event occurs afterwards
shodoco/bcc,mcaleavya/bcc,shodoco/bcc,romain-intel/bcc,tuxology/bcc,tuxology/bcc,romain-intel/bcc,iovisor/bcc,romain-intel/bcc,mcaleavya/bcc,iovisor/bcc,tuxology/bcc,iovisor/bcc,brendangregg/bcc,brendangregg/bcc,shodoco/bcc,brendangregg/bcc,iovisor/bcc,shodoco/bcc,mcaleavya/bcc,romain-intel/bcc,tuxology/bcc,iovisor/bcc,romain-intel/bcc,mcaleavya/bcc,shodoco/bcc,brendangregg/bcc,mcaleavya/bcc,tuxology/bcc,brendangregg/bcc