sunrpc: Update RPCBIND_MAXNETIDLEN

Commit 176e21ee ("SUNRPC: Support for RPC over AF_LOCAL
transports") added a 5-character netid, but did not bump
RPCBIND_MAXNETIDLEN from 4 to 5.

Fixes: 176e21ee ("SUNRPC: Support for RPC over AF_LOCAL ...")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/msg_prot.h

@@ -158,9 +158,9 @@ typedef __be32	rpc_fraghdr;
 
 /*
  * Note that RFC 1833 does not put any size restrictions on the
- * netid string, but all currently defined netid's fit in 4 bytes.
+ * netid string, but all currently defined netid's fit in 5 bytes.
  */
-#define RPCBIND_MAXNETIDLEN	(4u)
+#define RPCBIND_MAXNETIDLEN	(5u)
 
 /*
  * Universal addresses are introduced in RFC 1833 and further spelled