debuggerd: show syscall in SYS_SECCOMP one-liners.

The current logging...
```
F libc    : Fatal signal 31 (SIGSYS), code 1 (SYS_SECCOMP) in tid 6640 (logcat), pid 6640 (logcat)
```
...isn't super useful if crash_dump then fails, because you have no idea
what syscall caused the problem.

We already include the fault address in this line for relevant cases,
so include the syscall number in this case.

Bug: http://b/262391724
Test: treehugger
Change-Id: I45ad7d99c9904bab32b65efeb19be232e59ab3a4