Fix printing of invalid arguments of prctl syscall

Fix printing of invalid arguments of prctl syscall

* prctl.c (SYS_FUNC(prctl)): Print 2nd syscall argument
of PR_CAPBSET_DROP, PR_CAPBSET_READ, PR_CAP_AMBIENT, PR_MCE_KILL,
and PR_SET_SECCOMP using printxval_long.
Print 2nd syscall argument of PR_SET_SECUREBITS using printflags_long.
Print 3rd syscall argument of PR_CAP_AMBIENT and PR_MCE_KILL using
printxval_long.
* tests/prctl-seccomp-strict.c (main): Update.