Add support for string values with white spaces for ifconfig(8)

parameters accepting them (such as description, group).

Changes discussed on freebsd-rc.

PR:		conf/156675
Reported by:	"Alexander V. Chernikov" <melifaro att ipfw ru>
Suggested by:	hrs
Analyzed with:	Alexander V. Chernikov via IRC
MFC after:	2 weeks

etc/network.subr

@@ -94,7 +94,7 @@ ifconfig_up()
 	# ifconfig_IF
 	ifconfig_args=`ifconfig_getargs $1`
 	if [ -n "${ifconfig_args}" ]; then
-		ifconfig $1 ${ifconfig_args}
+		eval ifconfig $1 ${ifconfig_args}
 		_cfg=0
 	fi