openvswitch: Fix MPLS action validation.

Linux stack does not implement GSO for packet with multiple
encapsulations.  Therefore there was check in MPLS action
validation to detect such case, But this check introduced
bug which deleted one or more actions from actions list.
Following patch removes this check to fix the validation.

Fixes: 25cd9ba0 ("openvswitch: Add basic MPLS support to
kernel").

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Reported-by: Srinivas Neginhal <sneginha@vmware.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>