Rather than just unregistering the socket, we now actually close
the Connection. This ensures we never end up with an unregistered
but open connection.

src/hooks/dhcp/high_availability/ha_service.*
    HAService::clientConnectHandler() - modified to call
    HttpClient::closeIfOutOfBandwidth().

src/lib/http/client.*
    Connection - replaced isTransaction(int socket_fd) with
    isMySocket(int socket_fd)

    ConnectionPool - replaced isTransaction(int socket_fd) with
    closeIfOutOfBandwidth(int socket_fd)

    HttpClient - replaced isTransaction(int socket_fd) with
    closeIfOutOfBandwidth(int socket_fd)