Ethernet faces are not created after dropping privileges
In NFD 0.6.2 PPA package,
nfd.conf drops root privilege and
seteuid to "ndn" user, and the installation script executes
setcap on the NFD binary.
As reported in #4565-3, this is ineffective because
seteuid automatically clears all capabilities unless the
SECBIT_KEEP_CAPS flag is set on the process, and Ethernet face creation fails with "pcap_activate: You don't have permission to capture on that device" error.
To fix this issue,
PcapHelper should wrap