miniflow: Remove unused values_inline branch from miniflow_move()

The branch is unused as size < sizeof dst->inline_values must
always be true for inlined values. Hitting the branch would lead
to corruption as inline_values is accessed out of bounds.

Remove branch and add assertion.

Cc: Jarno Rajahalme <jrajahalme@nicira.com>
Signed-off-by: Thomas Graf <tgraf@noironetworks.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>