tcp: fix regression in urgent data handling

Stephan Springl found that commit 1402d366 "tcp: introduce
tcp_try_coalesce" introduced a regression for rlogin

It turns out problem comes from TCP urgent data handling and
a change in behavior in input path.

rlogin sends two one-byte packets with URG ptr set, and when next data
frame is coalesced, we lack sk_data_ready() calls to wakeup consumer.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Stephan Springl <springl-k@lar.bfw.de>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>