MIPv6: display Experimental Mobility Message Data as such

Bug: 10703
Change-Id: I9b16f503418d7464234be3c772b5dae3fb5eb7a9
Reviewed-on: https://code.wireshark.org/review/5378
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>
(cherry picked from commit 36837a2f5a340af6206dedf0245b4687fcc53254)
Reviewed-on: https://code.wireshark.org/review/5382