add macros offsetof and container_of
add macros offsetof and container_of

These are two common kernel macros to manipulate data
structures. Let us add them to helpers.h so bpf program
can use them.

Signed-off-by: Yonghong Song <e76892bbe783db2f627de1232e139db4de43da60@fb.com>

brendangregg/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc