bfdd: fix compilation warnings on OmniOS

bfdd: fix compilation warnings on OmniOS

Build will fail with `Werror` enabled with:

```
  CC       bfdd/bfdd_cli.o
In file included from ./lib/frratomic.h:21:0,
                 from ./lib/memory.h:22,
                 from ./lib/vector.h:25,
                 from ./lib/command.h:25,
                 from bfdd/bfdd_cli.c:23:
./config.h:665:0: error: "_FILE_OFFSET_BITS" redefined [-Werror]
 #define _FILE_OFFSET_BITS 64
 ^
In file included from /usr/include/iso/stdlib_iso.h:49:0,
                 from /usr/include/stdlib.h:37,
                 from ./lib/memory.h:20,
                 from ./lib/vector.h:25,
                 from ./lib/command.h:25,
                 from bfdd/bfdd_cli.c:23:
/opt/gcc-5.1.0/lib/gcc/i386-pc-solaris2.11/5.1.0/include-fixed/sys/feature_tests.h:231:0: note: this is the location of the previous definition
 #define _FILE_OFFSET_BITS 32
 ^
In file included from ./lib/thread.h:24:0,
                 from ./lib/vty.h:27,
                 from ./lib/command.h:26,
                 from bfdd/bfdd_cli.c:23:
./lib/zebra.h:271:2: error: #warning "assuming 4-byte alignment for CMSG_SPACE" [-Werror=cpp]
 #warning "assuming 4-byte alignment for CMSG_SPACE"
  ^
./lib/zebra.h:277:2: error: #warning "assuming 4-byte alignment for CMSG_LEN" [-Werror=cpp]
 #warning "assuming 4-byte alignment for CMSG_LEN"
  ^
cc1: all warnings being treated as errors
Makefile:6876: recipe for target 'bfdd/bfdd_cli.o' failed
gmake[1]: *** [bfdd/bfdd_cli.o] Error 1
```

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>