lsfd: fill ENDPOINTS column for FIFOs

lsfd: fill ENDPOINTS column for FIFOs

For FIFO type files, lsof can fill ENDPOINTS as following:

  _PID_,_COMMAND_,_ASSOC_[-r][-w]

Example output:

  $ dd if=/dev/zero | nc -l 127.0.0.1 9091 > /dev/null &
  [1] 1707808 1707809

  $ ./lsfd -p "1707808 1707809" -o+ENDPOINTS -Q '(type == "FIFO")'
  COMMAND     PID   USER ASSOC MODE TYPE SOURCE MNTID    INODE NAME            ENDPOINTS
  dd      1707808 yamato     1  -w- FIFO pipefs    14 73477636 pipe:[73477636] 1707809,nc,0r-
  nc      1707809 yamato     0  r-- FIFO pipefs    14 73477636 pipe:[73477636] 1707808,dd,1-w

Signed-off-by: Masatake YAMATO <yamato@redhat.com>