MFH: r448238

net/ostinato: Fix building on 11.1-RELEASE and HEAD

11.1-RELEASE and HEAD include libpcap 1.8 which doesn't ensure the experimental
remote packet capture feature only available to WIN32 isn't picked up by
builds on Unix. This solves the build error of the missing remote-ext.h
header file.

Approved by: portmgr (with hat)