ipsec-tools: Fix pfkey UPDATE failure caused by EINTR

While kernel is processing the UPDATE message which is sent from racoon,
it maybe interrupted by certain system signal and if this case happens,
kernel responds with an EINTR message to racoon and kernel fails to
establish the corresponding SA.
Fix this problem by resend the UPDATE message when EINTR(Interrupted
system call) error happens.

Signed-off-by: Xufeng Zhang <xufeng.zhang@windriver.com>
Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>