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: 5bb4c45d466c ("net/tls: Read sk_prot once when building tls proto ops")
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/tls/tls_main.c

···
 	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;