Reorder functions in syscall.c. No code changes.

Reorder functions in syscall.c. No code changes.

Old order (basically "in no particular order"):
    dumpio
    decode_subcall
    internal_syscall
    get_scno
    get_syscall_result
    known_scno
    syscall_fixup
    is_negated_errno
    get_error
    syscall_enter
    trace_syscall_entering
    trace_syscall_exiting
    trace_syscall
    printargs
    getrval2
    sys_indir
    is_restart_error

New order:
various utility functions:
    decode_subcall
    printargs
    getrval2
    sys_indir
    is_restart_error
syscall enter handling functions:
    get_scno
    known_scno
    syscall_fixup (also used in syscall exit code)
    internal_syscall (also used in syscall exit code)
    syscall_enter
    trace_syscall_entering
syscall exit handling functions:
    get_syscall_result
    is_negated_errno
    get_error
    dumpio
    trace_syscall_exiting
main syscall enter/exit function:
    trace_syscall

* syscall.c: Reorder functions so that related ones are closer
in the source.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>