like did on telescope 73bb7969cfc48e90a10200bd6b1c8c1ed9aff4f2 unfreeze the buffer by default ("melt" it :P)

port of telescope commit 1470eab31452d2fab50bc4965320dab7892b2ef3 original commit message: > on libevent2 we need to wrap evbuffer_add with > evbuffer_freeze/evbuffer_unfreeze. Not sure exactly why, probably > because we're doing some evbuffer_enable/disable/enable-again.