net: bonding: avoid using bash string replace

X-Gentoo-Bug: 359311
X-Gentoo-Bug-URL: http://bugs.gentoo.org/359311
Reported-by: Raffaello D. Di Napoli <fastijum@gmail.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

net/bonding.sh

@@ -100,9 +100,9 @@ bonding_pre_start()
 		if [ -n "${primary}" ]; then
 			echo "+${primary}" >/sys/class/net/"${IFACE}"/bonding/slaves
 			echo "${primary}" >/sys/class/net/"${IFACE}"/bonding/primary
-			slaves="${slaves/${primary}/}"
 		fi
 		for s in ${slaves}; do
+			[ "${s}" = "${primary}" ] && continue
 			echo "+${s}" >/sys/class/net/"${IFACE}"/bonding/slaves
 		done
 	else