dracut-module-setup.sh: use kernel exported mac address in kdump_get_mac_addr()

kernel has exported mac address for each interface, we can get it
directly instead of parsing the output from ip address show.

Signed-off-by: WANG Chao <chaowang@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>

dracut-module-setup.sh

@@ -83,7 +83,7 @@ kdump_static_ip() {
 }
 
 kdump_get_mac_addr() {
-    echo `ip addr show $1 2>/dev/null|awk '/ether/{ print $2 }'`
+    cat /sys/class/net/$1/address
 }
 
 #Bonding or team master modifies the mac address