net/tap: avoid using SIGIO
net/tap: avoid using SIGIO

SIGIO maybe used by application, instead choose another rt-signal.
Linux allows any signal to be used for signal based IO.
Search for an unused signal in the available rt-signal range.

Add more error checking for fcntl and signal handling.

Signed-off-by: Stephen Hemminger <06fa905d7f2aaced6dc72e9511c71a2a51e8aead@networkplumber.org>
Acked-by: Morten Brørup <77666125932addc6fc525b281b518fd8fd2203d8@smartsharesystems.com>
Reviewed-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk