l2tp: generate correct module alias strings

Commit 65b32f80 ("uapi: move IPPROTO_L2TP to in.h") moved the
definition of IPPROTO_L2TP from a define to an enum, but since
__stringify doesn't work properly with enums, we ended up breaking the
modalias strings for the l2tp modules:

 $ modinfo l2tp_ip l2tp_ip6 | grep alias
 alias:          net-pf-2-proto-IPPROTO_L2TP
 alias:          net-pf-2-proto-2-type-IPPROTO_L2TP
 alias:          net-pf-10-proto-IPPROTO_L2TP
 alias:          net-pf-10-proto-2-type-IPPROTO_L2TP

Use the resolved number directly in MODULE_ALIAS_*() macros (as we
already do with SOCK_DGRAM) to fix the alias strings:

$ modinfo l2tp_ip l2tp_ip6 | grep alias
alias:          net-pf-2-proto-115
alias:          net-pf-2-proto-115-type-2
alias:          net-pf-10-proto-115
alias:          net-pf-10-proto-115-type-2

Moreover, fix the ordering of the parameters passed to
MODULE_ALIAS_NET_PF_PROTO_TYPE() by switching proto and type.

Fixes: 65b32f80 ("uapi: move IPPROTO_L2TP to in.h")
Link: https://lore.kernel.org/lkml/ZCQt7hmodtUaBlCP@righiandr-XPS-13-7390


Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Tested-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>