Fix disabling of bold and fastblink

According to ECMA-48¹ 8.3.117, an attribute value of 21 is "doubly
underlined", while 22 is "normal colour or normal intensity (neither
bold nor faint)".

Additionally, 25 is "steady (not blinking)", which likely means neither
slow blink nor fast blink.

¹: http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-048.pdf

Signed-off-by: Roberto E. Vargas Caballero <k0ga@shike2.com>

st.c

@@ -1718,11 +1718,8 @@ tsetattr(int *attr, int l) {
 		case 9:
 			term.c.attr.mode |= ATTR_STRUCK;
 			break;
-		case 21:
-			term.c.attr.mode &= ~ATTR_BOLD;
-			break;
 		case 22:
-			term.c.attr.mode &= ~ATTR_FAINT;
+			term.c.attr.mode &= ~(ATTR_BOLD | ATTR_FAINT);
 			break;
 		case 23:
 			term.c.attr.mode &= ~ATTR_ITALIC;
@@ -1731,10 +1728,7 @@ tsetattr(int *attr, int l) {
 			term.c.attr.mode &= ~ATTR_UNDERLINE;
 			break;
 		case 25:
-			term.c.attr.mode &= ~ATTR_BLINK;
+			term.c.attr.mode &= ~(ATTR_BLINK | ATTR_FASTBLINK);
-			break;
-		case 26:
-			term.c.attr.mode &= ~ATTR_FASTBLINK;
 			break;
 		case 27:
 			term.c.attr.mode &= ~ATTR_REVERSE;