iwinfo: fix WPA cipher reporting

Within the Lua binding, use the same logic as the command line interface for
reporting the used WPA ciphers. Instead of printing the intersection of
pairwise and group ciphers, report both group and pairwise ciphers.

This fixes a case where a connection which uses CCMP for pairwise and TKIP
as groupwise cipher is getting reported as using the NONE cipher.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>