BZ #16529: Fix pedantic warning with netinet/in.h.

When compiling with pedantic the following warning is seen:

gcc -Wall -pedantic -O0 -o test test.c
In file included from test.c:3:0:
/path/inet/netinet/in.h:111:21: warning: comma at end of \
enumerator list [-Wpedantic]
     IPPROTO_MH = 135,      /* IPv6 mobility header.  */
                     ^

It is valid C99 to have a trailing comma after the last item in
an enumeration. However it is not valid C90. If possible glibc
attempts to keep all headers C90 + long long without requiring
C99 features. In this case it's easy to fix the headers and it
removes the warning seem with -pedantic.
Bug 6981 was fixed by commit 1484e65736f4cab27e5051e0f06be8470e69af82.
Bug 15968 was fixed by commit 0748546f660d27a2ad29fa6174d456e2f6490758.