ofproto-dpif: Fix uninitialized struct member in xlate_actions().

ofproto-dpif: Fix uninitialized struct member in xlate_actions().

Commit 7257b535ab "Implement new fragment handling policy." moved around
a bunch of initialization code in xlate_actions() so that the assignment
to ctx->flow.tp_src and .tp_dst would not have to also assign to
ctx->base_flow.tp_src and .tp_dst.  However, this meant that the early-exit
"return" in the new switch statement exited without initializing a lot of
the context.  In particular 'may_set_up_flow' didn't get initialized, so
something the early-exit would produce a flow that couldn't be installed,
which wasn't the intent.

It seems that this optimization was a bad tradeoff, so this commit puts
all of the initialization up front and just assigns to both copies of the
tp_src and tp_dst members.

Fixes a nondeterministic "make check" failure in the VLAN handling test.