init: harden socket creation against symlinks

Instead of using chown, use the symlink safe lchown.

Instead of using chmod, use the symlink safe fchmodat
with AT_SYMLINK_NOFOLLOW.

Fix a bug where the SELinux filesystem creation context may
not be restored, and some memory not freed, if bind() fails.

Check the return values from the chown/chmod calls and unlink
the files if it ever fails.

(cherrypicked from commit ab5629c1)

Bug: 27337831
Change-Id: I28c5f4dee55aa706437eb51ad403c1fbf56138de