lsfd: add ERROR as a new type

lsfd: add ERROR as a new type

lsfd ignored file descriptors with that readlink(2) or
stat(2) returned errors.

With ERORR type, lsfd can print these file descriptors with incomplete
information.

An example output:

   COMMAND        PID   USER ASSOC  XMODE  TYPE          SOURCE MNTID INODE NAME
   systemd      10677 yamato    31 ????-- ERROR readlink:EACCES
   slirp4netns 901147 yamato     7 ????-- ERROR     stat:EACCES             /home/yamato/.local/share/.../merged

The format of SOURCE column is SYSCALL:ERRNO.

The code for printing errno name is highly based on the code for
printing syscall name in enosys.c.

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