kernel/linux: fix using custom location

Currently, extract and patch are skipped as thus:
- using a custom directory of pre-installed headers
- a correctly named directory already exists

Otherwise, extract and patch are done.

The current second condition is wrong, because it allows the following
sequence to happen:
- a non-custom kernel is used
- a previous build only partially extracted the non-custom sources
- that p[revious build broke during extraction (eg. incomplete tarball...)
- a subsequent build will find a properly named directory, and will
thus skip extract and patch, which is wrong

Fix that by following the conditions in this table:

Type | Extract | Patch
----------------------+---------+-------
Pre-installed headers | N | N
custom directory | N | N
custom tarball | Y | N
mainstream tarball | Y | Y

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: David Holsgrove <david.holsgrove@xilinx.com>

 From: Tomoyoshi ASANO <asa@lineo.co.jp>

 Message ID: <20081208073522.0AEF.22C34B8C@lineo.co.jp>

 Hello,

 I have SEGV at busybox's telnet with uClibc-0.9.30.

 It seem the current uClibc-trunk has the same problem.

 Thanks,

 -- Tom

 diff -ru uClibc-0.9.30.orig/libc/inet/getaddrinfo.c uClibc-0.9.30/libc/inet/getaddrinfo.c

 --- uClibc-0.9.30.orig/libc/inet/getaddrinfo.c	2008-10-28 17:25:10.000000000 +0100

 +++ uClibc-0.9.30/libc/inet/getaddrinfo.c	2009-02-26 14:20:06.000000000 +0100

 @@ -186,7 +186,7 @@

  			return seen;

  		}

 -		for (runp = ifa; runp != NULL; runp = runp->ifa_next)

 +		for (runp = ifa; runp != NULL; runp = runp->ifa_next) {

  #if defined __UCLIBC_HAS_IPV4__

  			if (runp->ifa_addr->sa_family == PF_INET)

  				seen |= SEEN_IPV4;

 @@ -195,7 +195,7 @@

  			if (runp->ifa_addr->sa_family == PF_INET6)

  				seen |= SEEN_IPV6;

  #endif /* __UCLIBC_HAS_IPV6__ */

 -

 +                }

  		freeifaddrs(ifa);

  	}

  #else