udp: Avoid including netdb.h

netdb.h pulls in a large chain of include files:
rpc/netdb.h
rpc/types.h

rpc/types.h re-defines TRUE/FALSE and does it in this way:

 #ifndef FALSE
 #      define  FALSE   (0)
 #endif

 #ifndef TRUE
 #      define  TRUE    (1)
 #endif

And this later causes build problems that appear in this way:

mipsel-linux-gnu-gcc -Wall -DVER=1.8  -D_GNU_SOURCE -DHAVE_CLOCK_ADJTIME
-DHAVE_POSIX_SPAWN -DHAVE_ONESTEP_SYNC  -Os -pipe -mno-branch-likely
-mips32r2 -mtune=24kc -fno-caller-saves -Wno-unused-result
-D_FORTIFY_SOURCE=1 -Wl,-z,now -Wl,-z,relro
-I/home/florian/dev/openwrt/trunk/staging_dir/target-mipsel-unknown-linux-gnu_glibc/usr/include
-I/home/florian/dev/openwrt/trunk/staging_dir/target-mipsel-unknown-linux-gnu_glibc/include
-I/home/florian/dev/toolchains/stbgcc-4.8-1.5/usr/include
-I/home/florian/dev/toolchains/stbgcc-4.8-1.5/include
-DHAVE_CLOCK_ADJTIME -DHAVE_POSIX_SPAWN -DHAVE_ONESTEP_SYNC   -c -o
udp.o udp.c
In file included from
/home/florian/dev/openwrt/trunk/staging_dir/target-mipsel-unknown-linux-gnu_glibc/usr/include/rpc/netdb.h:45:0,
                 from
/home/florian/dev/toolchains/stbgcc-4.8-1.5/mipsel-linux-gnu/sys-root/usr/include/netdb.h:32,
                 from udp.c:23:
pdt.h:25:7: error: expected identifier before '(' token
 enum {FALSE, TRUE};
       ^
<builtin>: recipe for target 'udp.o' failed

Upon inspection, it does not appear that netdb.h is providing any useful
definition or declaration, so let's just remove its inclusion.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

udp.c

@@ -20,7 +20,6 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <net/if.h>
-#include <netdb.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <stdlib.h>

udp6.c

@@ -20,7 +20,6 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <net/if.h>
-#include <netdb.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <stdlib.h>