apparmor: change op from int to const char *

Having ops be an integer that is an index into an op name table is
awkward and brittle. Every op change requires an edit for both the
op constant and a string in the table. Instead switch to using const
strings directly, eliminating the need for the table that needs to
be kept in sync.

Signed-off-by: John Johansen <john.johansen@canonical.com>