Generalize seccomp filter parser

Generalize seccomp filter parser

Linux socket filter uses almost the same classic BPF as seccomp filter,
The only difference noticeable from strace PoV is the meaning of generic
multiuse field.

Transform the parser of seccomp filters to a more generic parser
of classic BPF, parametrized with a method of parsing the generic
multiuse field in BPF_STMT.

* bpf_filter.c: New file.
* bpf_filter.h: Likewise.
* bpf_fprog.h: Likewise.
* bpf_seccomp_filter.c: Likewise.
* fetch_bpf_fprog.c: Likewise.
* fetch_seccomp_fprog.c: Remove.
* seccomp_fprog.h: Likewise.
* Makefile.am (strace_SOURCES): Add bpf_filter.c, bpf_filter.h,
bpf_fprog.h, bpf_seccomp_filter.c, and fetch_bpf_fprog.c.
Remove fetch_seccomp_fprog.c and seccomp_fprog.h.
* seccomp.c: Do not include linux/filter.h and xlat header files.
Do not define SECCOMP_RET_ACTION.
(bpf_filter, decode_bpf_code, decode_bpf_stmt, decode_bpf_jump,
print_bpf_filter, print_seccomp_fprog, print_seccomp_filter): Remove.
* defs.h (print_seccomp_filter): Rename to decode_seccomp_fprog.
(SYS_FUNC(seccomp)): Replace print_seccomp_filter
with decode_seccomp_fprog.
* prctl.c (SYS_FUNC(prctl)): Likewise.