datapath: Fix type of actions_len_left in modify_vlan_tci().

datapath: Fix type of actions_len_left in modify_vlan_tci().

The sparse checker reported that the type of the pointer passed to
nla_next(), as &actions_len_left, was incorrect: whereas the parameter
has type "int *", &actions_len_left is an "unsigned int *".  This fixes
the problem.  It is not a bug fix since the code is equally correct (or
incorrect) either way, but it gets the types right anyhow.

I don't know why GCC was not reporting this as an error.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>