batctl: Dynamically select header format in netlink_print_neighbors

batctl: Dynamically select header format in netlink_print_neighbors

The netlink_print_neighbors() function previously used a static header
format, which did not account for variations between the neighbor list
output from different BATMAN routing algorithms (BATMAN_IV vs. BATMAN_V).

This change ensures that the table header output in `batctl n` is accurate
for both BATMAN routing algorithms.

Signed-off-by: Sven Eckelmann <sven@narfation.org>