Bump grpc to v1.51.0

Signed-off-by: Luca Comellini <luca.com@gmail.com>

vendor/google.golang.org/grpc/internal/resolver/unix/unix.go

@@ -49,8 +49,9 @@ func (b *builder) Build(target resolver.Target, cc resolver.ClientConn, _ resolv
 	}
 	addr := resolver.Address{Addr: endpoint}
 	if b.scheme == unixAbstractScheme {
-		// prepend "\x00" to address for unix-abstract
-		addr.Addr = "\x00" + addr.Addr
+		// We can not prepend \0 as c++ gRPC does, as in Golang '@' is used to signify we do
+		// not want trailing \0 in address.
+		addr.Addr = "@" + addr.Addr
 	}
 	cc.UpdateState(resolver.State{Addresses: []resolver.Address{networktype.Set(addr, "unix")}})
 	return &nopResolver{}, nil