freebsd.makefs: uncomment code which can copy rdev information from mtree (#360323)

The freebsd makefs code is imported directly from netbsd, with minor changes.

One of these changes is commenting out a piece of code we need in order to

cross-build filesystem images for openbsd with nix: the ability to copy device

node information from an mtree. This is especially important in nix because the

only other way to generate device nodes is to have them be resident on the

build system's filesystem, which is not possible without root, and openbsd does

not have a devfs and requires that all device nodes are simply present on the

root filesystem in order to boot.

Uncomment it.

diff --git a/usr.sbin/makefs/walk.c b/usr.sbin/makefs/walk.c

index 56e2d19c6f00..c3bf8faac2aa 100644

--- a/usr.sbin/makefs/walk.c

+++ b/usr.sbin/makefs/walk.c

@@ -540,12 +540,12 @@ apply_specentry(const char *dir, NODE *specnode, fsnode *dirnode)

 		dirnode->inode->st.st_flags = specnode->st_flags;

 	}

 #endif

-/*	if (specnode->flags & F_DEV) {

+	if (specnode->flags & F_DEV) {

 		ASEPRINT("rdev", "%#llx",

 		    (unsigned long long)dirnode->inode->st.st_rdev,

 		    (unsigned long long)specnode->st_rdev);

 		dirnode->inode->st.st_rdev = specnode->st_rdev;

-	}*/

+	}

 #undef ASEPRINT

 	dirnode->flags |= FSNODE_F_HASSPEC;