I frequently get frustrated when Wireshark won't run as a non-root user due to permissions on the dumpcap process. Here's the fix:
sudo groupadd wireshark
sudo usermod -a -G wireshark $USER
sudo chgrp wireshark /usr/bin/dumpcap
sudo chmod 754 /usr/bin/dumpcap
sudo setcap 'CAP_NET_RAW+eip CAP_NET_ADMIN+eip' /usr/bin/dumpcap
exec su -l $USER # reload groups for user
Alternatively, you can log out and log back in to refresh the groups the user is in.