Now that bpftool generates NULL definition as part of vmlinux.h, drop custom
NULL definition in skb_pkt_end.c.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20210317200510.1354627-3-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>