net/tls: fix const assignment warning

Building with some experimental patches, I came across a warning
in the tls code:

include/linux/compiler.h:215:30: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
  215 |  *(volatile typeof(x) *)&(x) = (val);  \
      |                              ^
net/tls/tls_main.c:650:4: note: in expansion of macro 'smp_store_release'
  650 |    smp_store_release(&saved_tcpv4_prot, prot);

This appears to be a legitimate warning about assigning a const pointer
into the non-const 'saved_tcpv4_prot' global. Annotate both the ipv4 and
ipv6 pointers 'const' to make the code internally consistent.

Fixes: 5bb4c45d ("net/tls: Read sk_prot once when building tls proto ops")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_main.c

@@ -56,9 +56,9 @@ enum {
 	TLS_NUM_PROTS,
 };
 
-static struct proto *saved_tcpv6_prot;
+static const struct proto *saved_tcpv6_prot;
 static DEFINE_MUTEX(tcpv6_prot_mutex);
-static struct proto *saved_tcpv4_prot;
+static const struct proto *saved_tcpv4_prot;
 static DEFINE_MUTEX(tcpv4_prot_mutex);
 static struct proto tls_prots[TLS_NUM_PROTS][TLS_NUM_CONFIG][TLS_NUM_CONFIG];
 static struct proto_ops tls_sw_proto_ops;