netfilter: built-in NAT support for DCCP, SCTP, UDPlite

Version 2 changes:
- use #ifdef ... in place of #if IS_ENABLED()
- add footprint test results

The above L4 protocols usually need an explicit modprobe command (e.g "modprobe nf_nat_proto_sctp") to provide full functionality of REDIRECT targets and SNAT/DNAT targets where port number translation is explicitly configured.
In order to remove such limitation, this series converts CONFIG_NF_NAT_PROTO_{DCCP,SCTP,UDPLITE} from tristate to boolean: in case NAT support for these protocols is enabled in the kernel configuration, it will be built into nf_nat.ko.

footprint test:

each patch of the series has been individually tested on a nf-next.git kernel with standard RHEL7 configuration on x86_64 architecture, recording the unstripped binary size after module clean/rebuild:

# ls -l net/netfilter/nf_nat{,_proto_{dccp,sctp,udplite}}.ko

(nf_nat_proto_) udplite | sctp | dccp || nf_nat
--------------------------------+--------+--------++------------

no builtin              408048  | 428344 | 409800 || 2241312
DCCP builtin            408048  | 428344 |   -    || 2578968
SCTP builtin            408048  |   -    | 409800 || 2597032
UDPLITE builtin           -     | 428344 | 409800 || 2577256
all builtin               -     |   -    |   -    || 3270616

Davide Caratti (3):
netfilter: built-in NAT support for DCCP
netfilter: built-in NAT support for SCTP
netfilter: built-in NAT support for UDPlite

 include/net/netfilter/nf_nat_l4proto.h |  9 +++++++++
 net/netfilter/Kconfig                  |  6 +++---
 net/netfilter/Makefile                 | 10 +++++-----
 net/netfilter/nf_nat_core.c            | 12 ++++++++++++
 net/netfilter/nf_nat_proto_dccp.c      | 36 +---------------------------------
 net/netfilter/nf_nat_proto_sctp.c      | 35 +--------------------------------
 net/netfilter/nf_nat_proto_udplite.c   | 35 +--------------------------------
 7 files changed, 32 insertions(+), 111 deletions(-)

2.5.5