Revert "net/sunrpc: Use static const char arrays"

This reverts commit 411b5e05.

Olga Kornievskaia reports:

Problem: linux client mounting linux server using rc4-hmac-md5
enctype. gssd fails with create a context after receiving a reply from
the server.

Diagnose: putting printout statements in the server kernel and
kerberos libraries revealed that client and server derived different
integrity keys.

Server kernel code was at fault due the the commit

[aglo@skydive linux-pnfs]$ git show 411b5e05

Trond: The problem is that since it relies on virt_to_page(), you cannot
call sg_set_buf() for data in the const section.
Reported-by: NOlga Kornievskaia <aglo@citi.umich.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org	[2.6.36+]

net/sunrpc/auth_gss/gss_krb5_mech.c

@@ -427,7 +427,7 @@ static int
 context_derive_keys_rc4(struct krb5_ctx *ctx)
 {
 	struct crypto_hash *hmac;
-	static const char sigkeyconstant[] = "signaturekey";
+	char sigkeyconstant[] = "signaturekey";
 	int slen = strlen(sigkeyconstant) + 1;	/* include null terminator */
 	struct hash_desc desc;
 	struct scatterlist sg[1];