net/dhcpd: Add ipv6-only-preferred option per RFC 8925

While here, pet linters.

PR:		275217
Reported by:	mallorya@fastmail.com
Approved by:	koue@chaosophia.net (maintainer)

net/dhcpd/Makefile

@@ -10,25 +10,22 @@ LICENSE=	BSD3CLAUSE
 
 USES=		ssl uidfix
 
-WRKSRC_SUBDIR=	src/usr.sbin/${PORTNAME}
-
 USE_GITHUB=	yes
 GH_ACCOUNT=	koue
-
-CONFLICTS=	isc-dhcp4[1-3]-server*
-
 USE_RC_SUBR=	dhcpd
 
-CFLAGS+=	-Wall
-
 MAKE_ARGS+=	BINDIR=${PREFIX}/sbin MANDIR=${PREFIX}/man/man
 
+CFLAGS+=	-Wall
+
+CONFLICTS=	isc-dhcp4[1-3]-server*
+WRKSRC_SUBDIR=	src/usr.sbin/${PORTNAME}
+
 OPTIONS_DEFINE=	NOPF
+OPTIONS_SUB=	yes
 
 NOPF_DESC=	Disable PF support
 
-OPTIONS_SUB=	yes
-
 NOPF_CFLAGS=	-DNO_PF=1
 
 post-patch:

net/dhcpd/files/patch-dhcp-options.5

@@ -0,0 +1,13 @@
+--- dhcp-options.5.orig	2020-04-13 17:07:01 UTC
++++ dhcp-options.5
+@@ -346,6 +346,10 @@ This option specifies whether the client should config
+ for packet forwarding.
+ A value of 0 means disable IP forwarding, and a value of 1 means enable
+ IP forwarding.
++.It Ic option ipv6-only-preferred Ar uint32 ;
++The number of seconds for which an IPv6-only-capable client should disable
++DHCPv4.
++See RFC 8925 for details.
+ .It Ic option irc-server Ar ip-address Oo , Ar ip-address ... Oc ;
+ The
+ .Ic irc-server

net/dhcpd/files/patch-tables.c

@@ -0,0 +1,11 @@
+--- tables.c.orig	2023-11-20 14:12:38 UTC
++++ tables.c
+@@ -184,7 +184,7 @@ struct option dhcp_options[256] = {
+ 	{ "option-105", "X",				&dhcp_universe, 105 },
+ 	{ "option-106", "X",				&dhcp_universe, 106 },
+ 	{ "option-107", "X",				&dhcp_universe, 107 },
+-	{ "option-108", "X",				&dhcp_universe, 108 },
++	{ "ipv6-only-preferred", "L",			&dhcp_universe, 108 },
+ 	{ "option-109", "X",				&dhcp_universe, 109 },
+ 	{ "option-110", "X",				&dhcp_universe, 110 },
+ 	{ "option-111", "X",				&dhcp_universe, 111 },