pcl: explicitly disable pcap

winpcap package is broken: it doesn't install many headers needed by normal
applications like pcl. If it is installed before `make pcl`, the pcl build
system falsely believes the installation is legit and tries to build against
winpcap, and fails.

Therefore, before fixing winpcap, it is better to at least make pcl build.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>