Fixed Memory Leak, Added Network Flags for Mumbai and Mainnet

In this release, we have fixed the memory leak issue in bor, added network flags that can be used while invoking bor and few other minor changes. Major changes are listed below:

• Memory Leak Fixed: The root cause for the memory leak was identified and fixed in #201. We had already fixed the memory bloat issue that was causing few nodes to consume the entire memory within minutes of starting bor in https://github.com/maticnetwork/bor/releases/tag/v0.2.9-beta1
• Network Flags: You can now start bor using bor --bor-mainnet and bor --bor-mumbai flags to connect to mainnet and mumbai networks respectively. The defaults can be found here: https://github.com/maticnetwork/bor/blob/6c7a9e1c410992486ce610ed3836cec35ba546e6/cmd/geth/config.go#L342-L386 and any params that need to be overridden can be passed separately.

Pre-requisites

Please upgrade the go version to v1.16 or above before updating.