lsof: correct check for symbolic link

lsof: correct check for symbolic link

Busybox lsof used the d_type field of a 'struct dirent' to verify whether the
entry is a symbolic link. This field, however, is not portable. On at least
one board [1] I have seen, that field is 0, and the check fails even though
the entry is a link.

The explicit check for a symbolic link is really only needed to skip the
default directory entries '.' and '..'. The directory /proc/<pid>/fd/
should not contain anything else but these two and symbolic links.
With these assumptions, this patch replaces the explicit link check with a
basic check for '.' and '..' (and any hidden file). In the unlikely case that
there are other file types, xmalloc_readlink() will return NULL, and we can
skip the entry.

[1] A MIPS-based board with glibc 2.9, Linux 2.6.32.27.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>