rxrpc: Fix oops from calling udpv6_sendmsg() on AF_INET socket

rxrpc: Fix oops from calling udpv6_sendmsg() on AF_INET socket

If rxrpc sees an IPv6 address, it assumes it can call udpv6_sendmsg() on it
- even if it got it on an IPv4 socket.  Fix do_udp_sendmsg() to give an
error in such a case.

general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
...
RIP: 0010:ipv6_addr_v4mapped include/net/ipv6.h:749 [inline]
RIP: 0010:udpv6_sendmsg+0xd0a/0x2c70 net/ipv6/udp.c:1361
...
Call Trace:
do_udp_sendmsg net/rxrpc/output.c:27 [inline]
do_udp_sendmsg net/rxrpc/output.c:21 [inline]
rxrpc_send_abort_packet+0x73b/0x860 net/rxrpc/output.c:367
rxrpc_release_calls_on_socket+0x211/0x300 net/rxrpc/call_object.c:595
rxrpc_release_sock net/rxrpc/af_rxrpc.c:886 [inline]
rxrpc_release+0x263/0x5a0 net/rxrpc/af_rxrpc.c:917
__sock_release+0xcd/0x280 net/socket.c:650
sock_close+0x18/0x20 net/socket.c:1365
__fput+0x27c/0xa90 fs/file_table.c:320
task_work_run+0x16b/0x270 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xb35/0x2a20 kernel/exit.c:820
do_group_exit+0xd0/0x2a0 kernel/exit.c:950
__do_sys_exit_group kernel/exit.c:961 [inline]
__se_sys_exit_group kernel/exit.c:959 [inline]
__x64_sys_exit_group+0x3a/0x50 kernel/exit.c:959

Fixes: ed472b0c8783 ("rxrpc: Call udp_sendmsg() directly")
Reported-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org