Fix a typo: Unidirected -> Undirected

As reported in https://ask.wireshark.org/questions/37462/possible-mistake-in-bluetooth-low-energy-hci-event-type

Change-Id: Ia6217531208b00c52c89bcb279cbbe67b5163e96
Reviewed-on: https://code.wireshark.org/review/5004
Reviewed-by: Michael Mann <mmann78@netscape.net>
(cherry picked from commit 3d9b35fab46812a4c718c0cbaa06ddd6f01f9e61)
Change-Id: Ia6217531208b00c52c89bcb279cbbe67b5163e96
Reviewed-on: https://code.wireshark.org/review/5007
Reviewed-by: Michael Mann <mmann78@netscape.net>