Add values to ExactMatch and WildcardMatch

[krsna1729]

We have constructed upf-epc - a basic 4G/5G userplane function using BESS. As part of this effort we tried to use existing modules as much as possible. One big gap we knew about (from previous exploration of BESS-P4 work) is ability to set values in the exact match and wildcard match tables. Today the only thing being stored is gate information. We have extended it to be able to store value and set metadata or update the packet based on it. This exactly reverse of key creation. We are instantiating it like this. Protobuf changes.

Is there interest in having this in BESS?

/cc @sangjinhan @melvinw @chris3torek