vnet.9: Rename vnet.9/vimage.9 to VNET.9/VIMAGE.9

Fix crossreferences to VNET(9) by correcting it's capitalization.

MFC after:	3 days
Reviewed by:	enji, ziaee
Closes:		https://github.com/freebsd/freebsd-src/pull/1848

contrib/kyua/doc/kyuafile.5.in

@@ -485,7 +485,7 @@ plain_test_program{name='the_test',
 .Ss FreeBSD jail execution environment
 The following example configures the test to be run within a temporary jail
 with
-.Xr vnet 9
+.Xr VNET 9
 support and the permission to create raw sockets:
 .Bd -literal -offset indent
 syntax(2)

share/man/man9/Makefile

@@ -417,7 +417,7 @@ MAN=	accept_filter.9 \
 	vn_deallocate.9 \
 	vn_fullpath.9 \
 	vn_isdisk.9 \
-	vnet.9 \
+	VNET.9 \
 	vnode.9 \
 	vnode_pager_setsize.9 \
 	vnode_pager_purge_range.9 \
@@ -2474,7 +2474,7 @@ MLINKS+=VOP_OPENCLOSE.9 VOP_CLOSE.9 \
 MLINKS+=VOP_RDWR.9 VOP_READ.9 \
 	VOP_RDWR.9 VOP_WRITE.9
 MLINKS+=VOP_REMOVE.9 VOP_RMDIR.9
-MLINKS+=vnet.9 vimage.9
+MLINKS+=VNET.9 VIMAGE.9
 MLINKS+=vref.9 VREF.9 \
 	vref.9 vrefl.9
 MLINKS+=vrele.9 vput.9 \