net/ip: fix compile break if disable NET_TCP

[anchao]

Summary

net/ip: fix compile break if disable NET_TCP

ipfrag/ipv4_frag.c: In function ‘ipv4_fragin’:
ipfrag/ipv4_frag.c:184:22: warning: ‘head’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  184 |   ipv4->len[1] = head->io_pktlen & 0xff;
      |                  ~~~~^~~~~~~~~~~
ipfrag/ipv4_frag.c:123:21: note: ‘head’ was declared here
  123 |   FAR struct iob_s *head;
      |                     ^~~~

devif/ipv6_input.c: In function ‘ipv6_in’:
devif/ipv6_input.c:60:33: error: ‘TCPIPv6BUF’ undeclared (first use in this function); did you mean ‘UDPIPv6BUF’?
   60 | #define PAYLOAD ((FAR uint8_t *)TCPIPv6BUF)
      |                                 ^~~~~~~~~~

nat/ipv4_nat.c: In function ‘ipv4_nat_inbound_icmp’: nat/ipv4_nat.c:67:30: error: ‘TCP_HDRLEN’ undeclared (first use in this function); did you mean ‘UDP_HDRLEN’?
   67 |   ((proto) == IP_PROTO_TCP ? TCP_HDRLEN : \
      |                              ^~~~~~~~~~
nat/ipv4_nat.c:323:47: note: in expansion of macro ‘L4_HDRLEN’
  323 |             inner_l4hdrlen = MIN(inner_l4len, L4_HDRLEN(inner->proto));
      |                                               ^~~~~~~~~

net/slip.c:865:29: warning: unused variable ‘priv’ [-Wunused-variable]
  865 |   FAR struct slip_driver_s *priv =
      |                             ^~~~
net/slip.c: In function ‘slip_rmmac’:
net/slip.c:895:29: warning: unused variable ‘priv’ [-Wunused-variable]
  895 |   FAR struct slip_driver_s *priv =
      |                             ^~~~

local/local_sendmsg.c: In function ‘local_sendmsg’:
local/local_sendmsg.c:423:18: warning: ‘count’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  423 |           return count;
      |                  ^~~~~
local/local_sendmsg.c:131:11: warning: ‘i’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  131 |   while (i-- > 0)
      |          ~^~
local/local_sendmsg.c:71:7: note: ‘i’ was declared here
   71 |   int i;
      |       ^

Signed-off-by: chao an anchao@xiaomi.com

Impact

N/A

Testing

disable CONFIG_NET_TCP

[pkarashchenko]

@anchao maybe it is reasonable to add some configuration to the code tree, so CI can catch a build break like this?

[anchao]

@anchao maybe it is reasonable to add some configuration to the code tree, so CI can catch a build break like this?

Yes, I added some rare config, please review #8455