Return no protocols if mask is supplied for unmaskable match

Return no protocols if mask is supplied for unmaskable match

Currently if a mask is supplied for an unmaskable match then NOT_REACHED()
is called. The effect of this for a user calling ovs-vsctl with a match
that includes a mask which is not permitted is to politely inform them of
the error of their ways by calling abort and segfaulting.

This patch takes an alternate approach to return no protocols which has the
has the effect when that ovs-vsctl is called with a match that includes a
mask which is not permitted an error message of the following form is
displayed.

ovs-ofctl: none of the usable flow formats (none) is among the allowed flow formats (OpenFlow10,NXM)

This patch also updates the ovs-ofctl test to test matches with masks
where possible.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>