[NET]: Fix net/core/skbuff.c gcc-3.2.3 compilation error

Compiling 2.6.22-rc1 with gcc-3.2.3 for i486 fails with:

  gcc -m32 -Wp,-MD,net/core/.skbuff.o.d  -nostdinc -isystem /home/mikpe/pkgs/linux-x86/gnu/lib/gcc-lib/i486-pc-linux-gnu/3.2.3/include -D__KERNEL__ -Iinclude  -include include/linux/autoconf.h -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -O2 -pipe -msoft-float -mregparm=3 -freg-struct-return -mpreferred-stack-boundary=4  -march=i486 -ffreestanding -maccumulate-outgoing-args -DCONFIG_AS_CFI=1  -Iinclude/asm-i386/mach-default -fomit-frame-pointer       -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(skbuff)"  -D"KBUILD_MODNAME=KBUILD_STR(skbuff)" -c -o net/core/skbuff.o net/core/skbuff.c
net/core/skbuff.c:648:1: directives may not be used inside a macro argument
net/core/skbuff.c:647:39: unterminated argument list invoking macro "memcpy"
net/core/skbuff.c: In function `pskb_expand_head':
net/core/skbuff.c:651: `memcpy' undeclared (first use in this function)
net/core/skbuff.c:651: (Each undeclared identifier is reported only once
net/core/skbuff.c:651: for each function it appears in.)
net/core/skbuff.c:651: syntax error before "skb"
make[2]: *** [net/core/skbuff.o] Error 1
make[1]: *** [net/core] Error 2
make: *** [net] Error 2

The patch below implements a simple workaround which is to
clone the offending memcpy() call and specialise it for the
two different scenarios.

Other workarounds are of course possible: e.g. bind the varying
parameter in a local variable, or use a macro or inline function
to perform the varying computation.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: David S. Miller <davem@davemloft.net>