It looks like tshark parser was broken at some point for
wlan.mesh.config.cap which is now (tshark 2.6.3) pointing to incorrect
field (same as wlan.mesh.config.ps_protocol). This used to work with
tshark 2.2.6.
For now, assume the capability field ends up being the last octet of the
frame.
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>