BBsim crashes when storing flows

fatal error: concurrent map writes
goroutine 21756 [running]:
runtime.throw(0xf5d754, 0x15)
/usr/local/go/src/runtime/panic.go:774 +0x72 fp=0xc000b3b1e0 sp=0xc000b3b1b0 pc=0x430f52
runtime.mapassign(0xdd1d60, 0xc000040690, 0xc000b3b3a0, 0x14)
/usr/local/go/src/runtime/map.go:588 +0x5c3 fp=0xc000b3b268 sp=0xc000b3b1e0 pc=0x410493
github.com/opencord/bbsim/internal/bbsim/devices.(*OltDevice).FlowAdd(0x17f15c0, 0x10ee340, 0xc0012274a0, 0xc000d1ca00, 0x17f15c0, 0xc0012274a0, 0xc000311b58)
/app/internal/bbsim/devices/olt.go:983 +0x1a71 fp=0xc000b3baf8 sp=0xc000b3b268 pc=0xc91a11
github.com/opencord/voltha-protos/v4/go/openolt._Openolt_FlowAdd_Handler(0xf348a0, 0x17f15c0, 0x10ee340, 0xc0012274a0, 0xc000d5d440, 0x0, 0x10ee340, 0xc0012274a0, 0xc000ca8340, 0xc8)
/app/vendor/github.com/opencord/voltha-protos/v4/go/openolt/openolt.pb.go:5021 +0x217 fp=0xc000b3bb68 sp=0xc000b3baf8 pc=0xa38377
google.golang.org/grpc.(*Server).processUnaryRPC(0xc0001bad00, 0x10fca60, 0xc000276480, 0xc0005c7800, 0xc0001b6960, 0x17e3d40, 0x0, 0x0, 0x0)
/app/vendor/google.golang.org/grpc/server.go:1082 +0x4fd fp=0xc000b3be20 sp=0xc000b3bb68 pc=0xa0f5ad
google.golang.org/grpc.(*Server).handleStream(0xc0001bad00, 0x10fca60, 0xc000276480, 0xc0005c7800, 0x0)
/app/vendor/google.golang.org/grpc/server.go:1405 +0xd25 fp=0xc000b3bf48 sp=0xc000b3be20 pc=0xa13385
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc00047e040, 0xc0001bad00, 0x10fca60, 0xc000276480, 0xc0005c7800)
/app/vendor/google.golang.org/grpc/server.go:746 +0xbb fp=0xc000b3bfb8 sp=0xc000b3bf48 pc=0xa2025b
runtime.goexit()
/usr/local/go/src/runtime/asm_amd64.s:1357 +0x1 fp=0xc000b3bfc0 sp=0xc000b3bfb8 pc=0x45ead1
created by google.golang.org/grpc.(*Server).serveStreams.func1
/app/vendor/google.golang.org/grpc/server.go:744 +0xa1