MFC r317730:
Add support for listen() call.

MFC r317731:
Add Socklent for handling args of type socklen_t.

MFC r317732:
Decode the third argument of socket().

MFC r317736:
Add support for [gs]etsockopt().

MFC r317737:
Decode the fourth argument of sendto and recvfrom call.

MFC r317739:
Add support for sendmsg() and recvmsg().

MFC r317747:
Add support for socket option names related to the IPPROTO_SCTP level.

MFC r317748:
Add support for socket option names related to the IPPROTO_IPV6 level.

MFC r317750:
Add support for sctp_generic_sendmsg() and sctp_generic_recvmsg().

MFC r317789:
Add support for socket option names related to the level IPPROTO_UDPLITE.

MFC r318879:
Improve the decoding of the third argument of the socket() call.

Decoding of the third argument depends on the first one. For doing this,
add a corresponding function to libsysdecode.

Thanks to jhb@ for suggesting this.