net/fonulator: Unbreak build on FreeBSD >= 12.0

/usr/lib/libpcap.a(pcap-rdmasniff.o): In function `rdmasniff_create':
/usr/src/contrib/libpcap/pcap-rdmasniff.c:370: undefined reference to `ibv_get_device_list'
/usr/src/contrib/libpcap/pcap-rdmasniff.c:405: undefined reference to `ibv_free_device_list'

http://beefy5.nyi.freebsd.org/data/120i386-default/499228/logs/errors/fonulator-2.0.1_2.log
http://beefy14.nyi.freebsd.org/data/120mips-quarterly/499227/logs/errors/fonulator-2.0.1_2.log