MINOR: splice: disable it when the system returns EBADF

MINOR: splice: disable it when the system returns EBADF

At least on a heavily patched 2.6.35.9, we can see splice() fail
with EBADF :

  recv(6, "789.123456789.123456789.12345678"..., 1049, 0) = 1049
  send(5, "HTTP/1.1 200\r\nContent-length: 10"..., 8030, MSG_DONTWAIT|MSG_NOSIGNAL|MSG_MORE) = 8030
  gettimeofday({1352717854, 515601}, NULL) = 0
  epoll_wait(0x3, 0x40221008, 0x7, 0)     = 0
  gettimeofday({1352717854, 515793}, NULL) = 0
  pipe([7, 8])                            = 0
  splice(0x6, 0, 0x8, 0, 0xfe12c, 0x3)    = -1 EBADF (Bad file descriptor)
  close(6)                                = 0

This clearly is a kernel issue since all FDs are valid here, so let's
simply disable splice() on the connection when this happens so that
the session correctly recovers from that issue using recv().