lib/, src/: Unconditionally call setgroups(2)

lib/, src/: Unconditionally call setgroups(2)

Call it regardless of having added any groups.  If the group list is the
same that getgroups(3) gave us, setgroups(3) will be a no-op, and it
simplifies the surrounding code, by removing the 'added' variable, and
allowing to call lsearch(3) instead of lfind(3).

Reviewed-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>