udhcp: add PXELINUX path prefix option (code 210) definition

Like d3092c99, this change adds support for the DHCP "path-prefix"
option, as defined in RFC 5071. We use the string identifer
"pxepathprefix".

Adding this option makes string parsing in the hook scripts simpler.

function                                             old     new   delta
dhcp_option_strings                                  255     269     +14
dhcp_optflags                                         72      74      +2

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/networking/udhcp/common.c b/networking/udhcp/common.c
index fe322db..bc41c8d 100644
--- a/networking/udhcp/common.c
+++ b/networking/udhcp/common.c
@@ -63,6 +63,7 @@
 	{ OPTION_U8                               , 0x85 }, /* DHCP_VLAN_PRIORITY */
 #endif
 	{ OPTION_STRING                           , 0xd1 }, /* DHCP_PXE_CONF_FILE */
+	{ OPTION_STRING                           , 0xd2 }, /* DHCP_PXE_PATH_PREFIX */
 	{ OPTION_6RD                              , 0xd4 }, /* DHCP_6RD           */
 	{ OPTION_STATIC_ROUTES | OPTION_LIST      , 0xf9 }, /* DHCP_MS_STATIC_ROUTES */
 	{ OPTION_STRING                           , 0xfc }, /* DHCP_WPAD          */
@@ -130,6 +131,7 @@
 	"vlanpriority" "\0"/* DHCP_VLAN_PRIORITY  */
 #endif
 	"pxeconffile" "\0" /* DHCP_PXE_CONF_FILE  */
+	"pxepathprefix" "\0" /* DHCP_PXE_PATH_PREFIX  */
 	"ip6rd" "\0"       /* DHCP_6RD            */
 	"msstaticroutes""\0"/* DHCP_MS_STATIC_ROUTES */
 	"wpad" "\0"        /* DHCP_WPAD           */