net: wwan: iosm: select CONFIG_RELAY

net: wwan: iosm: select CONFIG_RELAY

The iosm driver started using relayfs, but is missing the Kconfig
logic to ensure it's built into the kernel:

x86_64-linux-ld: drivers/net/wwan/iosm/iosm_ipc_trace.o: in function `ipc_trace_create_buf_file_handler':
iosm_ipc_trace.c:(.text+0x16): undefined reference to `relay_file_operations'
x86_64-linux-ld: drivers/net/wwan/iosm/iosm_ipc_trace.o: in function `ipc_trace_subbuf_start_handler':
iosm_ipc_trace.c:(.text+0x31): undefined reference to `relay_buf_full'
x86_64-linux-ld: drivers/net/wwan/iosm/iosm_ipc_trace.o: in function `ipc_trace_ctrl_file_write':
iosm_ipc_trace.c:(.text+0xd5): undefined reference to `relay_flush'
x86_64-linux-ld: drivers/net/wwan/iosm/iosm_ipc_trace.o: in function `ipc_trace_port_rx':

Fixes: 00ef32565b9b ("net: wwan: iosm: device trace collection using relayfs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Reviewed-by: M Chetan Kumar <m.chetan.kumar@linux.intel.com>
Link: https://lore.kernel.org/r/20211204174033.950528-1-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>