systemd: Fix busctl crash on aarch64 when setting output table format

systemd: Fix busctl crash on aarch64 when setting output table format

The enum used for column names is integer type while table_set_display() is parsing
arguments on size_t alignment which may result in assert in table_set_display() if
the size between types missmatch. This patch cast the enums to size_t.
It also fixes all other occurences for table_set_display() and
table_set_sort().

Change-Id: Ie225491ae3f9752183d6ea7993d02ef450ed6ab6