libpcap: add rpcapd as package

libpcap: add rpcapd as package

This enables building of rpcapd and adds it as a package.

It is a daemon that allows remote packet capturing from another machine.
E.g. Wireshark can talk to it using the Remote Capture Protocol (RPCAP).
https://www.tcpdump.org/manpages/rpcapd.8.html

Compile and run tested: OpenWrt SNAPSHOT r17190-2801fe6132 on x86/64

Signed-off-by: Stephan Schmidtmer <hurz@gmx.org>