While convenient, avoid using alloca() for reasons specified in
the BUGS section of the alloca(3) manpage. In particular, when
the number of TCP sockets is several tens of thousand, trying to
"sysctl -a" would SIGSEGV on the net.inet.tcp.pcblist entry (it
would exceed the stacksize ulimit, in an undetectable manner).

Reported by: Igor Sysoev