net/realtek-re-kmod: fix build on FreeBSD 15.

I've opted for the simplest patch, the inclusion of if_private.h,
instead of a more invasive switch to IfAPI, to keep minimal changes
to vendor branch, hoping in a next vendor update to it.

net/realtek-re-kmod/Makefile

@@ -19,6 +19,12 @@ GH_ACCOUNT=	alexdupre
 GH_PROJECT=	rtl_bsd_drv
 GH_TAGNAME=	ea4ed1e
 
+.include <bsd.port.options.mk>
+
+.if ${OPSYS} == FreeBSD && (${OSVERSION} >= 1500000)
+EXTRA_PATCHES+= ${FILESDIR}/extra-patch-if__re.c
+.endif
+
 PLIST_FILES=	${KMODDIR}/if_re.ko
 
 .include <bsd.port.mk>

net/realtek-re-kmod/files/extra-patch-if__re.c

@@ -0,0 +1,10 @@
+--- if_re.c.orig	2024-06-04 09:39:04 UTC
++++ if_re.c
+@@ -67,6 +67,7 @@ __FBSDID("$FreeBSD: src/sys/dev/re/if_re.c,v " RE_VERS
+ 
+ #include <net/if.h>
+ #include <net/if_var.h>
++#include <net/if_private.h>
+ #include <net/if_arp.h>
+ #include <net/ethernet.h>
+ #include <net/if_dl.h>