tty/n_gsm: fix bug in tiocmset
tty/n_gsm: fix bug in tiocmset

Clear bitmask was not inverted before masking modem_tx.

Calling ioctl(fd, TIOCMBIC, TIOCM_RTS) results in:

[  197.430000] pre_modem_tx:	0x00000006
[  197.430000] clear:			0x00000004
[  197.430000] set:			0x00000000
[  197.440000] post_modem_tx:	0x00000004

which is wrong.

Signed-off-by: Nikola Diklic-Perin <d16233eece6408c5b77c48051a4028b0a502d8b5@gmail.com>
Acked-by: Alan Cox <91e38e63b890fbb214c8914809fde03c73e7f24d@linx.intel.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@suse.de>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs