scripts/tags.sh: Add BPF_CALL

Signed-off-by: Constantine Shulyupin <const@MakeLinux.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>