busybox: Split syslog initscript into busybox-syslog

busybox: Split syslog initscript into busybox-syslog

The same is already done for httpd and udhcpd.

This fixes Busybox deb upgrades: the prerm script was failing because
the last command "/etc/init.d/syslog stop", added by the update-rc.d
class, runs after the /bin/sh symlink has been removed.

Many images expect busybox to contain the syslog initscript, so busybox
RRECOMMENDS busybox-syslog.

busybox-{syslog,httpd,udhcpd} now RDEPEND on busybox, for consistency
with other packages in the recipe (e.g. busybox-mdev).

Signed-off-by: Michael Smith <msmith@cbnco.com>