linking against the socket stack is broken in 3.4.0

[yomimono]

See mirage/ocaml-git#280 (comment) for the original report (thanks @dinosaure ).

After mirage configure -t unix --net=socket and make depend:

~/mirage-skeleton/device-usage/network$ make
mirage build
ocamlfind: Package `tcp_socket_options' not found - required by `tcpip.tcpv4-socket'
ocamlfind ocamldep -package tcpip.unix -package tcpip.udpv4-socket -package tcpip.tcpv4-socket -package tcpip.stack-socket -package tcpip -package mirage-unix -package mirage-types-lwt -package mirage-types -package mirage-runtime -package mirage-logs -package mirage-clock-unix -package lwt -package functoria-runtime -predicates mirage_unix -modules main.ml > main.ml.depends
+ ocamlfind ocamldep -package tcpip.unix -package tcpip.udpv4-socket -package tcpip.tcpv4-socket -package tcpip.stack-socket -package tcpip -package mirage-unix -package mirage-types-lwt -package mirage-types -package mirage-runtime -package mirage-logs -package mirage-clock-unix -package lwt -package functoria-runtime -predicates mirage_unix -modules main.ml > main.ml.depends
ocamlfind: Package `tcp_socket_options' not found - required by `tcpip.tcpv4-socket'